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🧠 Solving LeetCode Until I Become Top 1% — Day `44`


This content originally appeared on DEV Community and was authored by Md. Rishat Talukder

🔹 Problem: 3136 Valid Word

Difficulty: #Easy
Tags: #String, #Validation, #Implementation

📝 Problem Summary

Given a string, check if it’s a valid “word” based on several conditions:

  • It must be at least 3 characters long.
  • It can only contain English letters (a-z, A-Z) and digits (0-9).
  • It must contain at least one vowel.
  • It must contain at least one consonant.

🧠 My Thought Process

  • Initial Thoughts:
    I jumped into it assuming the conditions were just “contains a vowel, consonant, and maybe digit” — and wrote code based on that.
    Spoiler: I didn’t read the question properly.

  • Bug Discovered:
    My solution failed on "aya" — which should be valid, but I thought it wasn’t because I misunderstood the rules.

  • Realization:
    After carefully re-reading the prompt, I realized I missed 3 critical conditions:

    • Word length must be ≥ 3
    • Only alphanumeric characters allowed
    • Must contain both vowel & consonant

  • Final Approach:
    Just iterate over the string, check character types one by one, and track flags for:

    • Is there a vowel?
    • Is there a consonant?
    • Is every character valid?

⚙ Code Implementation (Python) 

class Solution:
    def isValid(self, word: str) -> bool:
        if len(word) < 3:
            return False

        vowels = set('aeiouAEIOU')
        has_vowel = False
        has_consonant = False

        for c in word:
            if not c.isalnum():
                return False
            if c.isalpha():
                if c in vowels:
                    has_vowel = True
                else:
                    has_consonant = True

        return has_vowel and has_consonant

⏱ Time & Space Complexity

  • Time: O(n) — single pass through the word
  • Space: O(1) — only a few flags

🧩 Key Takeaways

  • ✅ Don’t assume what the problem is asking — read every line.
  • 💡 Even an easy string problem can go wrong if you skip rules.
  • 💭 In future string validation problems, always extract rules first before touching code.

🔁 Reflection (Self-Check)

  • [x] Could I solve this without help? (Eventually, after reading properly)
  • [x] Did I write code from scratch?
  • [x] Did I understand why it works?
  • [x] Will I be able to recall this in a week? (Yes, but I’ll also double check the prompt from now on.)

📚 Related Problems

🚀 Progress Tracker

Metric Value
Day 44
Total Problems Solved 385
Confidence Today 😐
Leetcode Rating 1572


This content originally appeared on DEV Community and was authored by Md. Rishat Talukder