LeetCode:Evaluate Reverse Polish Notation

题目链接

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

分析：这一题就是写程序计算逆波兰式的结果，遍历表达式，碰到操作数入栈，碰到操作符就从栈顶取出两个操作数，再将计算后的结果入栈，最后栈中剩余的唯一操作数就是计算结果。 本文地址

class Solution {
public:
int evalRPN(vector<string> &tokens) {
// IMPORTANT: Please reset any member data you declared, as
// the same Solution instance will be reused for each test case.
int len = tokens.size();
stack<int> S;
for(int i = 0; i < len; i++)
{
if(tokens[i] == "+" || tokens[i] == "-" ||
tokens[i] == "*" || tokens[i] == "/")
{
int op2 = S.top(); S.pop();
int op1 = S.top(); S.pop();
S.push( op(op1, op2, tokens[i][0]) );
}
else
S.push(stoi(tokens[i]));
}
return S.top();
}
int op(int op1, int op2, char optor)
{
if(optor == '+')return op1 + op2;
else if(optor == '-')return op1 - op2;
else if(optor == '*')return op1 * op2;
else return op1 / op2;
}
};

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