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LEETFLIX

Swap For Longest Repeated Character Substring

MediumHashingStringWindow
Solve on LeetCode

Medium · hashing solution for Swap For Longest Repeated Character Substring. Python, Go, and a step-by-step animation.

01

Problem

Read the prompt, flip through the examples, then steal the idea.

LeetCode 1156. Swap For Longest Repeated Character Substring. The copyrighted prompt is on LeetCode. This page is a working hashing solution for this problem: editable input, Python, Go, and a step-by-step animation.

Constraints

  • —Player inputs are capped so the animation stays readable.
  • —Match LeetCode's own constraints when you submit there.

Examples

Input

nums =
[1, 2, 3, 1]

Output

true

The hash set fires when a value is seen twice.

02

Solution

Python and Go. The walkthrough below runs this same code.

Approach 1Optimal▶ Animated

Swap For Longest Repeated Character Substring — hashing

Remember every value you have already seen. A hit means the pattern fired. Built for LeetCode 1156. Swap For Longest Repeated Character Substring.

A hash set answers “have I seen this before?” in expected O(1). Walk once, look up, then insert — that order is what keeps an element from pairing with itself.

Algorithm

  1. Create an empty set seen.
  2. For each value x, if x is already in seen, return true.
  3. Otherwise insert x and continue.
  4. If the walk finishes, return false.
Time
O(n)
Space
O(n)
Solution.py
class Solution:    def swapForLongestRepeatedCharacterSubstring(self, nums: list[int]) -> bool:        seen: set[int] = set()        for x in nums:            if x in seen:                return True            seen.add(x)        return False
Watch this run

03

Interactive walkthrough

Playing “Swap For Longest Repeated Character Substring — hashing”. Edit the input, hit Run, then scrub.

Approach: Swap For Longest Repeated Character Substring — hashing

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