{"id":849,"date":"2025-08-06T11:31:30","date_gmt":"2025-08-06T06:01:30","guid":{"rendered":"https:\/\/codeanddebug.in\/blog\/?p=849"},"modified":"2025-08-06T11:32:14","modified_gmt":"2025-08-06T06:02:14","slug":"valid-parentheses","status":"publish","type":"post","link":"https:\/\/codeanddebug.in\/blog\/valid-parentheses\/","title":{"rendered":"Valid Parentheses | Leetcode 20 | Stack implementation"},"content":{"rendered":"\n

The\u00a0Valid Parentheses<\/strong>\u00a0problem is a classic interview question to check your understanding of stacks and string parsing. It evaluates whether a given string consisting of parentheses\u2014()<\/code>,\u00a0{}<\/code>,\u00a0[]<\/code>, is well-formed. This guide provides a clear explanation, an easy-to-follow Python solution, and complexity analysis.<\/p>\n\n\n\n

Here’s the [Problem Link<\/span><\/mark><\/a><\/strong>] to begin with.<\/p>\n\n\n\n

Problem Statement<\/h2>\n\n\n\n

Given a string s<\/code> containing just the characters '('<\/code>, ')'<\/code>, '{'<\/code>, '}'<\/code>, '['<\/code>, and ']'<\/code>, determine if the input string is valid.<\/p>\n\n\n\n

An input string is valid if:<\/p>\n\n\n\n

    \n
  1. Open brackets are closed by the same type of brackets.<\/li>\n\n\n\n
  2. Open brackets are closed in the correct order.<\/li>\n\n\n\n
  3. Every close bracket has a corresponding open bracket.<\/li>\n<\/ol>\n\n\n\n

    Example<\/h3>\n\n\n\n
    <\/circle><\/circle><\/circle><\/g><\/svg><\/span><\/path><\/path><\/svg><\/span>
    Input: s = <\/span>"()[]<\/span>{}<\/span>"<\/span><\/span>\nOutput: true<\/span><\/span>\n<\/span>\nInput: s = <\/span>"(]"<\/span><\/span>\nOutput: false<\/span><\/span>\n<\/span>\nInput: s = <\/span>"([)]"<\/span><\/span>\nOutput: false<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
    Intuition & Approach<\/h2>\n\n\n\n
    The problem naturally maps to a stack<\/strong> data structure:<\/p>\n\n\n\n