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LEETFLIX

Find Substring With Given Hash Value

HardStringWindowHashing
Solve on LeetCode

Hard · sliding window solution for Find Substring With Given Hash Value. Python, Go, and a step-by-step animation.

01

Problem

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

LeetCode 2156. Find Substring With Given Hash Value. The copyrighted prompt is on LeetCode. This page is a working sliding window 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

s =
abcabcbb

Output

3

The longest unique window is abc (length 3).

02

Solution

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

Approach 1Optimal▶ Animated

Find Substring With Given Hash Value — sliding window

Grow right, shrink left the moment the window breaks its invariant. Built for LeetCode 2156. Find Substring With Given Hash Value.

The window [left, right] is the longest suffix ending at right that still obeys the rule (here: all unique). Last-seen indices tell you exactly how far to jump left.

Algorithm

  1. Walk right across the string.
  2. If s[right] was already inside the window, jump left past its last index.
  3. Record the last-seen index and update the best length.
Time
O(n)
Space
O(σ)
Solution.py
class Solution:    def findSubstringWithGivenHashValue(self, s: str) -> int:        last: dict[str, int] = {}        left = 0        best = 0        for right, ch in enumerate(s):            if ch in last and last[ch] >= left:                left = last[ch] + 1            last[ch] = right            best = max(best, right - left + 1)        return best
Watch this run

03

Interactive walkthrough

Playing “Find Substring With Given Hash Value — sliding window”. Edit the input, hit Run, then scrub.

Approach: Find Substring With Given Hash Value — sliding window

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