LeetCode 2 Evaluate Reverse Polish Notation

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

解析，利用栈结构，正确解析后缀表达式的顺序，应该是从左到直右扫描之后，在进行计算时，计算的次序于原来后缀表达式的次序相同，否则会发现除以零的错误！

public class Solution {    public int evalRPN(String[] tokens) {		Deque<Integer> stack = new ArrayDeque<Integer>();		for (int i = 0; i < tokens.length; i++) {			if ((tokens[i].charAt(0) >= '0' && tokens[i].charAt(0) <= '9')					|| (tokens[i].charAt(0) == '-' && tokens[i].length() > 1)) {				stack.push(Integer.parseInt(tokens[i]));			} else {				int x = stack.pop();				int y = stack.pop();				switch (tokens[i].charAt(0)) {				case '+':					stack.push(y + x);					break;				case '-':					stack.push(y - x);					break;				case '*':					stack.push(y * x);					break;				case '/':					stack.push(y / x);					break;				default:					break;				}			}		}		return stack.pop();	}}