Valid Parentheses

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.

Solution:

  1. public class Solution {
  2.   public boolean isValid(String s) {
  3.     char[] p = "(){}[]".toCharArray();
  4.     Map<Character, Character> map = new HashMap<>();
  6.     for (int i = 0; i < p.length - 1; i += 2) 
  7.       map.put(p[i + 1], p[i]);
  9.     Stack<Character> stack = new Stack<>();
  11.     for (char c : s.toCharArray()) {
  12.       if (c == '(' || c == '{' || c == '[')
  13.         stack.push(c);
  14.       else if (stack.isEmpty() || stack.peek() != map.get(c))
  15.         return false;
  16.       else
  17.         stack.pop();
  18.     }
  20.     return stack.isEmpty();
  21.   }
  22. }