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Check if two strings are isomorphic

Determine whether two strings are isomorphic by ensuring a one-to-one mapping between characters.

Python practice16 minHashing & SetsIntermediateLast updated March 26, 2026

Problem statement

Two strings s and t are isomorphic if characters in s can be replaced to get t, with a one-to-one mapping (no two characters map to the same character unless identical). Given two strings s and t, determine if they are isomorphic. Return True if they are, otherwise False.

Task

Use hashing (dictionaries) to validate a bijective mapping from characters of one string to another.

Examples

Basic mapping

Input

s = 'egg', t = 'add'

Output

True

e -> a, g -> d, consistent mapping exists and is one-to-one.

Input format

Two strings s and t.

Output format

Boolean value True if s and t are isomorphic, otherwise False.

Constraints

0 <= len(s), len(t) <= 10^5. Strings contain ASCII characters. Must run in O(n) time and O(1) additional space for mappings (alphabet-size bound).

Samples

Sample 1

Input

s = 'paper', t = 'title'

Output

True

p->t, a->i, p mapped consistently, e->l, r->e. Mapping is bijective.