20. Valid Parentheses

标签：determine   null   nta   pop   must   ==   sam   pen   ini   

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

An input string is valid if:

Open brackets must be closed by the same type of brackets.
Open brackets must be closed in the correct order.
Note that an empty string is also considered valid.

Example 1:

Input: "()"
Output: true
Example 2:

Input: "()[]{}"
Output: true
Example 3:

Input: "(]"
Output: false
Example 4:

Input: "([)]"
Output: false
Example 5:

Input: "{[]}"
Output: true

class Solution {
    public boolean isValid(String s) {
        if(s == null) return false;
        Stack<Character> stack = new Stack<>();
        String left = "([{";
        String right = ")]}";
        for(int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);
            if(left.indexOf(c) != -1) {
                stack.push(c);
            } 
            else{
                int index = right.indexOf(c);
                // char ctop = stack.pop();
                if(stack.isEmpty() || stack.peek() != left.charAt(index)){
                    return false;
                }
                stack.pop();
            }
        }
        return stack.isEmpty();
    }
}

20. Valid Parentheses

标签：determine   null   nta   pop   must   ==   sam   pen   ini   

原文地址：https://www.cnblogs.com/lawrenceSeattle/p/10255277.html