LeetCode:Evaluate Reverse Polish Notation

Evaluate Reverse Polish Notation

Total Accepted: 66669 Total
Submissions: 278014 Difficulty: Medium

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

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思路：

逆波兰表达式。

java code:

public class Solution {
public int evalRPN(String[] tokens) {

Stack<Integer> stack = new Stack<>();
int ans = 0;
int x, y;
for(String t : tokens) {
switch(t){
case "+":
stack.push(stack.pop() + stack.pop());
break;
case "-":
x = stack.pop();
y = stack.pop();
stack.push(y - x);
break;
case "*":
stack.push(stack.pop() * stack.pop());
break;
case "/":
x = stack.pop();
y = stack.pop();
stack.push(y / x);
break;
default:
stack.push(Integer.parseInt(t));
}
}
return stack.pop();
}
}