LeetCode | Evaluate Reverse Polish Notation

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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

后缀表达式，用栈做，遇到运算符出栈两个元素做运算，然后把结果入栈。switch（“字符串”）是jdk1.7的新特性。

代码如下：public class Solution {    public int evalRPN(String[] tokens) {        int temp = 0;        MyStack ms = new MyStack();        for(int i=0; i<tokens.length; i++){            switch(tokens[i]){                case "+": temp = ms.pop() + ms.pop(); ms.push(temp);break;                case "-": temp = -ms.pop() + ms.pop(); ms.push(temp);break;                case "*": temp = ms.pop() * ms.pop(); ms.push(temp);break;                case "/": temp = ms.pop();temp = ms.pop() / temp; ms.push(temp);break;                default: temp = Integer.parseInt(tokens[i]); ms.push(temp);            }        }        return ms.pop();    }}class MyStack{    int[] stack = new int[1000000];    int top = 1;    int pop(){        if(top == 0) return 0;        top--;        return stack[top];    }    void push(int a){        if(top > stack.length)            return;        stack[top] = a;        top++;    }}

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