LeetCode | Valid Parentheses

题目

Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.

The brackets must close in the correct order, "()" and "()[]{}" are all valid but "(]" and "([)]" are not.

分析

这种括号匹配用栈很方便，这里在判断括号是否匹配时利用了ASCII码的大小。

代码

import java.util.Stack;

public class ValidParentheses {
	public boolean isValid(String s) {
		Stack<Character> stack = new Stack<Character>();
		for (int i = 0; i < s.length(); ++i) {
			char c = s.charAt(i);
			if (c == '(' || c == '[' || c == '{') {
				stack.push(c);
			} else {
				if (stack.isEmpty() || c - stack.pop() > 2) {
					return false;
				}
			}
		}
		return stack.isEmpty();
	}
}