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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

Constraints:​

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

Code​

java Code


public boolean isValid(String s) {
    Stack<Character> stack = new Stack<Character>();
    for (char c : s.toCharArray()) {
        if (c == '(')
            stack.push(')');
        else if (c == '{')
            stack.push('}');
        else if (c == '[')
            stack.push(']');
        else if (stack.isEmpty() || stack.pop() != c)
            return false;
    }
    return stack.isEmpty();
}