題目:
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:
求解逆波蘭表達(dá)式,從公式中提取字符串,如果是操作數(shù)就push進(jìn)棧中,如果是操作符就從棧中pop出兩個(gè)數(shù),用第二個(gè)數(shù)和第一個(gè)數(shù)做運(yùn)算.
AC代碼:
//求解逆波蘭表達(dá)式
class Solution {
public:
int evalRPN(vector<string>& tokens) {
stack<int> num;
for(auto token:tokens){
if(token == "+" || token == "-" || token == "*"||token == "/"){
int a, b, ans;
b = num.top(); num.pop();
a = num.top(); num.pop();
if(token == "+")
ans = a + b;
if(token == "-")
ans = a - b;
if(token == "*")
ans = a * b;
if(token == "/")
ans = a / b;
num.push(ans);
}
else{
num.push(stoi(token));
}
}
return num.top();
}
};
