This content originally appeared on DEV Community and was authored by Md. Rishat Talukder
🔹 Problem: 1957. Delete Characters to Make Fancy String
Difficulty: #Easy
Tags: #String
📝 Problem Summary
Given a string s, remove the minimum number of characters such that there are no three consecutive characters that are the same. Return the resulting string.
✅ The answer is guaranteed to be unique.
🧠 My Thought Process
Brute Force Idea:
I initially tried to simulate the string modification by scanning it and usingpop(i)whenever I found three repeating characters. But... yeah,pop()on a list is O(n) if it's not at the end — and I was doing it potentiallyntimes. So... it timed out.-
Optimized Strategy:
I realized instead of deleting from the original string, I could build a new one from scratch:- Start with an empty result list.
- Loop through each character.
- Append the character only if the last two characters in the result are not equal to the current character.
This way, I never have three in a row — and all operations are fast (O(1) per append/check).
- Algorithm Used: Simple greedy + string construction strategy.
⚙️ Code Implementation (Python)
class Solution:
def makeFancyString(self, s: str) -> str:
res = []
for c in s:
if len(res) >= 2 and res[-1] == res[-2] == c:
continue
res.append(c)
return ''.join(res)
⏱️ Time & Space Complexity
- Time: O(n) — One pass through the string with constant time operations.
- Space: O(n) — To store the resulting string.
🧩 Key Takeaways
- ✅ Reversing your approach can turn a brute force into a greedy O(n) solution.
- 💡 Avoid modifying a list in-place with
pop(i)inside a loop unless you're popping from the end. - 💭 If a problem talks about "consecutive" characters, consider a sliding window of size 2 or 3.
🔁 Reflection (Self-Check)
- [x] Could I solve this without help?
- [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?
📚 Related Problems
- [[3316 Find Maximum Removals From Source String]]
🚀 Progress Tracker
| Metric | Value |
|---|---|
| Day | 50 |
| Total Problems Solved | 391 |
| Confidence Today | 😃 |
| Leetcode Rating | 1572 |
This content originally appeared on DEV Community and was authored by Md. Rishat Talukder
Md. Rishat Talukder | Sciencx (2025-07-21T09:37:42+00:00) 🧠 Solving LeetCode Until I Become Top 1% — Day `50`. Retrieved from https://www.scien.cx/2025/07/21/%f0%9f%a7%a0-solving-leetcode-until-i-become-top-1-day-50/
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