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Valid Parentheses

Problem Statement​

Given a string s 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.
  • Every close bracket has a corresponding open bracket of the same type.

Leetcode Link

Example 1:​

Input: s = "()"
Output: true

Example 2:​

Input: s = "()[]{}"
Output: true

Example 3:​

Input: s = "(]"
Output: false

Constraints:​

  • 1 <= s.length <= 104
  • s consists of parentheses only '()[]{}'.

Code​

Java Code

class Solution {
    public boolean isValid(String s) {
        char [] arr = s.toCharArray();
    Stack stack = new Stack();
    for(char ch : arr){
        if(stack.isEmpty()){
            stack.push(ch);
        }else{
            char top = (char)stack.lastElement();
            if(ch - top == 1 || ch - top == 2){
                stack.pop();
            }else{
                stack.push(ch);
            }
        }
    }
    if(stack.isEmpty()){
        return true;
    }
    return false;

    }
}