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LeetCode MEDIUM 3 Longest Substring Without Repeating Characters Summary

2026-04-10 694 words 4 minutes #leetcode

Generated by Codex with GPT-5

Quick facts

Difficulty: MEDIUM
Problem: Longest Substring Without Repeating Characters
Main tags: Hash Table, String, Sliding Window

What the problem is really asking

Given a string, the goal is to find the length of the longest contiguous block of characters with no repeats.

The important word is contiguous. This is not asking for a subsequence that can skip characters. It is asking for one unbroken window inside the string.

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LeetCode MEDIUM 5 Longest Palindromic Substring Summary

2026-04-10 821 words 4 minutes #leetcode

Generated by Codex with GPT-5

Quick facts

Difficulty: MEDIUM
Problem: Longest Palindromic Substring
Frequency: 64.1
Main tags: Two Pointers, String, Dynamic Programming

What the problem is really asking

Given a string, return the longest contiguous substring that reads the same forward and backward.

The word “substring” is the important constraint. This is not about picking scattered characters. The answer has to be one continuous block inside the original string.

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LeetCode MEDIUM 560 Subarray Sum Equals K Summary

2026-04-10 678 words 4 minutes #leetcode

Generated by Codex with GPT-5

Quick facts

Difficulty: MEDIUM
Problem: Subarray Sum Equals K
Main tags: Array, Hash Table, Prefix Sum

What the problem is really asking

The input is an integer array and a target k.

The task is not to find the longest subarray or to return the subarray itself. It is simply to count how many contiguous subarrays add up to k.

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