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This is a medium difficulty Coding & Algorithms question, commonly asked during Technical Screen rounds at TikTok.

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This question is commonly asked for Machine Learning Engineer candidates at TikTok during technical interviews.

Find length of longest common subsequence

Last updated: Mar 29, 2026

Quick Overview

This question evaluates understanding of dynamic programming, string algorithms, and algorithmic problem-solving skills related to sequence comparison and the longest common subsequence concept.

TikTok

Jan 22, 2026, 12:00 AM

Machine Learning Engineer

Technical Screen

Coding & Algorithms

Given two strings s and t, return the length of their longest common subsequence.

A subsequence is obtained by deleting zero or more characters without changing the relative order of the remaining characters.

Input

s : string
t : string

Output

Integer length of the longest common subsequence of s and t .

Constraints (typical)

0 <= len(s), len(t) <= 2000
Strings consist of lowercase English letters (or ASCII characters).

Example

s = "abcde" , t = "ace" → output 3 (one LCS is "ace" ).

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