算法训练营Day21|227.基本计算器

学习任务

依旧栈的经典应用。 题目链接：https://leetcode.cn/problems/basic-calculator-ii/description/ 优秀题解：https://leetcode.cn/problems/basic-calculator-ii/solutions/91271/chai-jie-fu-za-wen-ti-shi-xian-yi-ge-wan-zheng-ji-/

class Solution { public: int calculate(string s) { vector<int> stk; char preSign = '+'; int num = 0; int n = s.length(); for (int i = 0; i < n; ++i) { if (isdigit(s[i])) { num = num * 10 + int(s[i] - '0'); } if (!isdigit(s[i]) && s[i] != ' ' || i == n - 1) { switch (preSign) { case '+': stk.push_back(num); break; case '-': stk.push_back(-num); break; case '*': stk.back() *= num; break; default: stk.back() /= num; } preSign = s[i]; num = 0; } } return accumulate(stk.begin(), stk.end(), 0); } };