O(n) time and O(1) space using hashset.

Author: 149ps

205. Isomorphic Strings/205. Isomorphic Strings.py

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+"""
+Given two strings s and t, determine if they are isomorphic.
+
+Two strings are isomorphic if the characters in s can be replaced to get t.
+
+All occurrences of a character must be replaced with another character while preserving the order of characters. No two characters may map to the same character but a character may map to itself.
+
+Example 1:
+
+Input: s = "egg", t = "add"
+Output: true
+Example 2:
+
+Input: s = "foo", t = "bar"
+Output: false
+Example 3:
+
+Input: s = "paper", t = "title"
+Output: true
+Note:
+You may assume both s and t have the same length.
+"""
+
+
+class Solution:
+    def isIsomorphic(self, s: str, t: str) -> bool:
+        hset = set()
+        for i, j in zip(s, t):
+            if not (i, j) in hset:
+                hset.add((i, j))
+        return len(hset) == len(set(s)) == len(set(t))