readme.md

Leetcode

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

Solution

package leetcode20_ValidParentheses;

import java.util.Stack;

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