🎉 feat: initial commit for leetcode 762 using bitset

Author: liuchuo

C++/762. Prime Number of Set Bits in Binary Representation.cpp

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+762. Prime Number of Set Bits in Binary Representation
+Given two integers L and R, find the count of numbers in the range [L, R] (inclusive) having a prime number of set bits in their binary representation.
+(Recall that the number of set bits an integer has is the number of 1s present when written in binary. For example, 21 written in binary is 10101 which has 3 set bits. Also, 1 is not a prime.)
+Example 1:
+Input: L = 6, R = 10
+Output: 4
+Explanation:
+6 -> 110 (2 set bits, 2 is prime)
+7 -> 111 (3 set bits, 3 is prime)
+9 -> 1001 (2 set bits , 2 is prime)
+10->1010 (2 set bits , 2 is prime)
+Example 2:
+Input: L = 10, R = 15
+Output: 5
+Explanation:
+10 -> 1010 (2 set bits, 2 is prime)
+11 -> 1011 (3 set bits, 3 is prime)
+12 -> 1100 (2 set bits, 2 is prime)
+13 -> 1101 (3 set bits, 3 is prime)
+14 -> 1110 (3 set bits, 3 is prime)
+15 -> 1111 (4 set bits, 4 is not prime)
+Note:
+L, R will be integers L <= R in the range [1, 10^6].
+R - L will be at most 10000.
+
+题目大意：给两个数L和R，在[L, R]区间寻找数字的二进制中1的个数是素数的数字个数
+分析：R不超过10的6次方，也就是不超过2的20次方，那么判断是否为素数只需判断是否等于2 3 5 7 11 13 17 19即可，用bitset也只需20位表示即可，用count函数计算1的个数，然后用cnt统计后返回～
+
+class Solution {
+public:
+    int countPrimeSetBits(int L, int R) {
+        int cnt = 0, hash[20] = {0, 0, 1, 1, 0, 1, 0, 1, 0, 0, 0, 1, 0, 1, 0, 0, 0, 1, 0, 1};
+        for (int i = L; i <= R; i++) {
+            bitset<20> b(i);
+            if(hash[b.count()]) cnt++;
+        }
+        return cnt;
+    }
+};