Evaluate the value of an arithmetic expression in Reverse Polish Notation.
Valid operators are +
, -
, *
, /
.
Each operand may be an integer or another expression.
Some examples:
["2", "1", "+", "3", "*"] -> ((2 + 1) * 3) -> 9 ["4", "13", "5", "/", "+"] -> (4 + (13 / 5)) -> 6
class Solution { public: int str2int(string token){ int num=0; int start=0; int isNev = 1; //判断符号 if(token[0]=='-'){isNev=-1; start++;} else if(token[0]=='+')start++; for(int i=start; i<token.length(); i++){ num=10*num+(token[i]-'0'); } return num*isNev; } bool isOp(string token){ if(token=="/" || token=="+" || token=="-" || token=="*") return true; } int evalRPN(vector<string> &tokens) { stack<int> st; for(int i=0; i<tokens.size(); i++){ if(isOp(tokens[i])){ //如果是运算符,则计算栈顶元素,然后将结果入栈 int val1 = st.top(); st.pop(); int val2 = st.top(); st.pop(); int res = 0; if(tokens[i]=="+") res = val2 + val1; else if(tokens[i]=="-") res = val2 - val1; else if(tokens[i]=="*") res = val2 * val1; else if(tokens[i]=="/") res = val2 / val1; //计算结果入栈 st.push(res); } else{ //数字入栈 st.push(str2int(tokens[i])); } } return st.top(); } };
LeetCode: Evaluate Reverse Polish Notation [150],布布扣,bubuko.com
LeetCode: Evaluate Reverse Polish Notation [150]
原文地址:http://blog.csdn.net/harryhuang1990/article/details/36204735