Add C++ solutions for leetcode 227.

Author: Bruce Yang

cpp-leetcode/leetcode227-basic-calculator-ii_stack1.cpp

@@ -0,0 +1,60 @@
+#include <algorithm>
+#include <string>
+#include <vector>
+#include <iostream>
+using namespace std;
+// 特点: 没有括号, 使用栈来做
+class Solution {
+public:
+    int calculate(string s) {
+        string temp;
+        for (auto ch : s)
+        {
+            if (ch != ' ')
+                temp.push_back(ch);
+        }
+        s = "+" + temp;
+
+        int len = s.size();
+        vector<int> nums;
+
+        for (int i=0; i < len; i++)
+        {
+            if (s[i] == '+' || s[i] == '-')
+            {
+                int j = i+1; // 找出"+200"这种结构中的数字
+                while (j < len && isdigit(s[j])) j++; // 循环结束时, j多跑了1位
+                int endPos = j-1;
+                int num = stoi(s.substr(i+1, endPos-(i+1)+1));                                
+                if (s[i] == '+') nums.push_back(num);
+                else nums.push_back(-num);
+                i = endPos;
+            }
+            else if (s[i] == '*' || s[i] == '/')
+            {
+                int j = i+1; // 找出"*100"这种结构中的数字
+                while (j < len && isdigit(s[j])) j++;
+                int endPos = j-1;
+                int num = stoi(s.substr(i+1, endPos-(i+1)+1));  
+                if (s[i] == '*')                     
+                    nums.back() = nums.back() * num;
+                else nums.back() = nums.back() / num;             
+                i = endPos;                
+            }
+        }
+        int sum = 0;
+        for (int i=0; i < nums.size(); i++) sum += nums[i];
+        return sum;
+    }
+};
+
+// Test
+int main()
+{
+    Solution sol;
+    string s = " 3+5 / 2 ";
+    auto res = sol.calculate(s);
+    cout << res << endl;
+
+    return 0;
+}

cpp-leetcode/leetcode227-basic-calculator-ii_stack2.cpp

@@ -0,0 +1,57 @@
+#include <algorithm>
+#include <string>
+#include <vector>
+#include <iostream>
+#include <numeric>   /* 含有 accumulate 函数 */
+using namespace std;
+
+// 特点: 没有括号, 使用栈来做
+class Solution {
+public:
+    int calculate(string s) {
+        auto spaceEndIts = remove(s.begin(), s.end(), ' ');
+        s.erase(spaceEndIts, s.end());
+        s = "+" + s;
+
+        int len = s.size();
+        vector<int> nums;
+
+        for (int i=0; i < len; i++)
+        {
+            if (s[i] == '+' || s[i] == '-')
+            {
+                int j = i+1; // 找出"+200"这种结构中的数字
+                while (j < len && isdigit(s[j])) j++; // 循环结束时, j多跑了1位
+                int endPos = j-1;
+                int num = stoi(s.substr(i+1, endPos-(i+1)+1));                                
+                if (s[i] == '+') nums.push_back(num);
+                else nums.push_back(-num);
+                i = endPos;
+            }
+            else if (s[i] == '*' || s[i] == '/')
+            {
+                int j = i+1; // 找出"*100"这种结构中的数字
+                while (j < len && isdigit(s[j])) j++;
+                int endPos = j-1;
+                int num = stoi(s.substr(i+1, endPos-(i+1)+1));  
+                if (s[i] == '*')                     
+                    nums.back() = nums.back() * num;
+                else nums.back() = nums.back() / num;             
+                i = endPos;                
+            }
+        }
+        int sum = accumulate(nums.begin(), nums.end(), 0);
+        return sum;
+    }
+};
+
+// Test
+int main()
+{
+    Solution sol;
+    string s = " 3+5 / 2 ";
+    auto res = sol.calculate(s);
+    cout << res << endl;
+
+    return 0;
+}