【leetcode】150. Evaluate Reverse Polish Notation

【leetcode】150. Evaluate Reverse Polish Notation

简单的逆波兰表达式，用栈模拟。

/*** @author          johnsondu* @problem         Evaluate Reverse Polish Notation* @url             /* @timeComlexity   O(n)* @spaceComplexity O(1)* @strategy        Reverse Polish Notation, simple simulation* @status          Accepted, runtime beats 29.57% of cpp submissions. 16ms* @time            20:12, Oct 21 2015*/class Solution {
public:int transfer(const string& digits) {int cnt = 0;int idx = 0;if(digits[0] == '-') idx ++;for(int i = idx; i < digits.size();  i ++)cnt = cnt * 10 + digits[i] - '0';if(idx) cnt = -cnt;return cnt;}int evalRPN(vector<string>& tokens) {stack<int> nums;for(int i = 0; i < tokens.size(); i ++) {if(tokens[i][0] >= '0' && tokens[i][0] <= '9' || tokens[i].size() > 1) {nums.push(transfer(tokens[i]));}else {int rt = p(); nums.pop();int lf = p(); nums.pop();switch(tokens[i][0]) {case '+':nums.push(lf + rt);continue;case '-':nums.push(lf - rt);continue;case '*':nums.push(lf * rt);break;default:nums.push(lf / rt);continue;}}}p();}
};