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();
    }
}