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‎algorithm_interview_course/chapter_two/section_2.cpp

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/* ************************************************************************
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> File Name: algorithm_2.cpp
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> Author: sunxiuyang
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> Mail: [email protected]
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> Created Time: Thu Jan 30 16:09:35 2020
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> Description:
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************************************************************************/
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#include <iostream>
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#include <chrono>
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#include <thread>
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using namespace std;
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using namespace chrono;
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// O(n)
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void function1(long long n) {
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long long k = 0;
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for (long long i = 0; i < n; i++) {
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k++;
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}
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}
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// O(n^2)
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void function2(long long n) {
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long long k = 0;
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for (long long i = 0; i < n; i++) {
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for (long j = 0; j < n; j++) {
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k++;
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}
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}
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}
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// O(nlogn)
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void function3(long long n) {
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long long k = 0;
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for (long long i = 0; i < n; i++) {
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for (long long j = 1; j < n; j = j*2) { // 注意这里j=1
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k++;
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}
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}
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}
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void time_test() {
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long long n; // 数据规模
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while (cin>>n) {
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milliseconds start_time = duration_cast<milliseconds >(
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system_clock::now().time_since_epoch()
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);
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function3(n);
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milliseconds end_time = duration_cast<milliseconds >(
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system_clock::now().time_since_epoch()
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);
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cout << milliseconds(end_time).count() - milliseconds(start_time).count()
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<<" ms"<< endl;
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}
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}
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int main() {
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time_test();
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}
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‎algorithm_interview_course/chapter_two/section_3.cpp

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/* ************************************************************************
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> File Name: section_3.cpp
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> Author: sunxiuyang
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> Mail: [email protected]
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> Created Time: Sat Feb 8 22:00:32 2020
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> Description:
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************************************************************************/
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#include<iostream>
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using namespace std;
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int function1(int x, int n) {
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int result = 1; // 注意 任何数的0次方等于1
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for (int i = 0; i < n; i++) {
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result = result * x;
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}
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return result;
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}
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int function2(int x, int n) {
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if (n == 0) {
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return 1; // return 1 同样是因为0次方是等于1的
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}
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return function2(x, n - 1) * x;
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}
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int function3(int x, int n) {
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if (n == 0) {
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return 1;
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}
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// if (n == 1) { // 这里如果不作处理就会陷入死循环
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// return x;
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// }
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if (n % 2 == 1) {
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return function3(x, n/2) * function3(x, n/2) * x;
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}
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return function3(x, n/2) * function3(x, n/2);
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}
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int function4(int x, int n) {
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if (n == 0) {
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return 1;
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}
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int t = function4(x, n/2);
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if (n % 2 == 1) {
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return t*t*x;
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}
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return t*t;
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}
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int main() {
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int x, n;
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while (cin >> x >> n) {
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cout << function3(x, n) << endl;
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}
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}

‎algorithm_interview_course/chapter_two/section_4.cpp

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/* ************************************************************************
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> File Name: section_4.cpp
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> Author: sunxiuyang
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> Mail: [email protected]
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> Created Time: Tue Feb 18 23:34:08 2020
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> Description:
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************************************************************************/
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#include<iostream>
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using namespace std;
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struct node{
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int num;
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char cha;
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}st;
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int main() {
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int a[100];
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char b[100];
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cout << sizeof(int) << endl;
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cout << sizeof(char) << endl;
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cout << sizeof(a) << endl;
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cout << sizeof(b) << endl;
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cout << sizeof(st) << endl;
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}

‎algorithm_interview_course/chapter_two/section_5.cpp

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/* ************************************************************************
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> File Name: section_5.cpp
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> Author: sunxiuyang
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> Mail: [email protected]
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> Created Time: Mon Feb 24 18:44:56 2020
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> Description:
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************************************************************************/
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#include <iostream>
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#include <chrono>
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#include <thread>
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using namespace std;
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using namespace chrono;
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int fibonacci_1(int n) {
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if (n <= 0) {
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return 0;
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}
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if (n == 1 || n == 2) {
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return 1;
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}
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int first = 1, second = 1;
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int sum = first + second;
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for (int i = 2; i < n; i++) {
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sum = first + second;
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first = second;
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second = sum;
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}
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return sum;
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}
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int fibonacci_2(int i) {
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if(i <= 0) return 0;
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if(i == 1) return 1;
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return fibonacci_2(i - 1) + fibonacci_2(i - 2);
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}
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int fibonacci_3(int first, int second, int n) {
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if (n <= 0) {
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return 0;
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}
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if (n < 3) {
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return 1;
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}
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else if (n == 3) {
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return first + second;
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}
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else {
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return fibonacci_3(second, first + second, n - 1);
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}
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}
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void test_fibonacci() {
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int n;
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while(cin >> n) {
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cout << fibonacci_1(n) << endl;
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cout << fibonacci_2(n) << endl;
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cout << fibonacci_3(1, 1, n) << endl;
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}
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}
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int binary_search(int arr[], int l, int r, int n) {
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if (r >= l) {
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int mid = l + (r - l) / 2;
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if (arr[mid] == n)
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return mid;
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if (arr[mid] > n)
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return binary_search(arr, l, mid - 1, n);
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return binary_search(arr, mid + 1, r, n);
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}
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return -1;
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}
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int arr[] = {2, 3, 4, 5, 8, 10, 15, 17, 20};
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int binary_search(int l, int r, int n) {
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if (r >= l) {
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int mid = l + (r - l) / 2;
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if (arr[mid] == n)
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return mid;
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if (arr[mid] > n)
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return binary_search(l, mid - 1, n);
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return binary_search(mid + 1, r, n);
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}
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return -1;
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}
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void test_binary_search(void) {
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int arr[] = {2, 3, 4, 5, 8, 10, 15, 17, 20};
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int x = 17;
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int n = sizeof(arr) / sizeof(arr[0]);
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// int result = binary_search(arr, 0, n - 1, x);
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int result = binary_search(0, n - 1, x);
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(result == -1) ? cout << "Element is not present in array"
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: cout << "Element is present at index " << result;
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}
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int main()
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{
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// test_binary_search();
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// test_fibonacci();
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return 0;
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}
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‎algorithm_interview_course/chapter_two/section_6.cpp

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#include <iostream>
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#include <chrono>
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#include <thread>
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using namespace std;
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using namespace chrono;
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int fibonacci_2(int i) {
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if(i <= 0) return 0;
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if(i == 1) return 1;
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return fibonacci_2(i - 1) + fibonacci_2(i - 2);
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}
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void time_consumption() {
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int n;
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while (cin >> n) {
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milliseconds start_time = duration_cast<milliseconds >(
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system_clock::now().time_since_epoch()
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);
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fibonacci_2(n);
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milliseconds end_time = duration_cast<milliseconds >(
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system_clock::now().time_since_epoch()
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);
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cout << milliseconds(end_time).count() - milliseconds(start_time).count()
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<<" ms"<< endl;
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}
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}
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int main()
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{
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time_consumption();
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return 0;
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}
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‎problems/0000.TwoSum.md

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## 题目地址
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https://leetcode-cn.com/problems/two-sum/
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## 思路
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## 一般解法
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代码：
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```C++
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```
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## 优化解法
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```C++
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class Solution {
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public:
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vector<int> twoSum(vector<int>& nums, int target) {
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for (int i = 0; i < nums.size(); i ++) {
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for (int j = i + 1; j < nums.size(); j++) {
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if (nums[i] + nums[j] == target) {
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return {i, j};
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}
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}
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}
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return {};
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}
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};
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```
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```
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class Solution {
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public:
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vector<int> twoSum(vector<int>& nums, int target) {
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std::map <int,int> map;
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for(int i = 0; i < nums.size(); i++) {
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auto iter = map.find(target - nums[i]);
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if(iter != map.end()) {
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return {iter->second,i};
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}
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map[nums[i]] = i;
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}
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return {};
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}
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};
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```
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```
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class Solution {
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public:
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vector<int> twoSum(vector<int>& nums, int target) {
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std::unordered_map <int,int> map;
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for(int i = 0; i < nums.size(); i++) {
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auto iter = map.find(target - nums[i]);
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if(iter != map.end()) {
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return {iter->second, i};
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break;
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}
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map.emplace(nums[i], i);
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}
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return {};
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}
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};
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```
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## 代码
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```C++
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```

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