LeetCode - Evaluate Reverse Polish Notation

题意

思路

代码

class Solution {

stack<int> stk;

public:

int evalRPN(vector<string> &tokens)

{

vector<string>::iterator it;

for (it = tokens.begin(); it != tokens.end(); it++)

    {

string tmp = *it;

if (isdigit(tmp[0]) || (tmp[0] == '-' && tmp.size() != 1)) stk.push(Convert(tmp));

else

{                   

int b = stk.top(); stk.pop();

int a = stk.top(); stk.pop();

int c;

if (tmp[0] == '+') c = a + b;

    else if(tmp[0] == '-') c = a - b;

    else if (tmp[0] == '*') c = a * b;

    else c = a / b;

stk.push(c);

}

}

return stk.top();

}

int Convert(string str);

};

int Solution::Convert(string str)

{

int ans = 0, sig = 1;

if (str[0] == '-') sig = -1;

for (int i = 0; i < str.size(); i++)

if (isdigit(str[i])) ans = ans * 10 + str[i] - '0';

return ans * sig;

}