LeetCode

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.

思路：

用栈来解决。

package ds;

import java.util.Stack;

public class ValidParentheses {

    public boolean isValid(String s) {
        Stack<Character> stack = new Stack<Character>();
        int len = s.length();
        for (int i = 0; i < len; ++i) {
            char c = s.charAt(i);
            switch (c) {
            case '(':
                
            case '[':
                
            case '{':
                stack.push(c);
                break;
            case ')':
                if (stack.isEmpty() || stack.pop() != '(')
                    return false;
                break;
            case ']':
                if (stack.isEmpty() || stack.pop() != '[')
                    return false;
                break;
            case '}':                
                if (stack.isEmpty() || stack.pop() != '{')
                    return false;
                break;
            }
        }
        
        return stack.isEmpty();
    }
    
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        ValidParentheses v = new ValidParentheses();
        // Test case 1
        System.out.println(v.isValid("()[]}"));
        // Test case 2
        System.out.println(v.isValid("("));
    }

}