diff --git a/.plan b/.plan
new file mode 100644
index 0000000..513d90c
--- /dev/null
+++ b/.plan
@@ -0,0 +1,5 @@
+Sep 1, 2024
+
+complete top interview 150
+
+* solve "205. Isomorphic Strings"
diff --git a/src/isomorphic_strings.py b/src/isomorphic_strings.py
new file mode 100644
index 0000000..a8dda24
--- /dev/null
+++ b/src/isomorphic_strings.py
@@ -0,0 +1,16 @@
+class Solution:
+    def isIsomorphic(self, s: str, t: str) -> bool:
+        taken: set[str] = set()
+        translation: dict[str, str] = {}
+
+        for a, b in zip(s, t):
+            if a not in translation:
+                if b in taken:
+                    return False
+
+                translation[a] = b
+                taken.add(b)
+            elif translation[a] != b:
+                return False
+
+        return True
diff --git a/tests/test_isomorphic_strings.py b/tests/test_isomorphic_strings.py
new file mode 100644
index 0000000..c407a5f
--- /dev/null
+++ b/tests/test_isomorphic_strings.py
@@ -0,0 +1,16 @@
+import pytest
+
+from src.isomorphic_strings import Solution
+
+
+@pytest.mark.parametrize(
+    "expected,s,t",
+    (
+        (True, "egg", "add"),
+        (False, "foo", "bar"),
+        (True, "paper", "title"),
+        (False, "badc", "baba"),
+    ),
+)
+def test_solution(expected, s, t):
+    assert expected is Solution().isIsomorphic(s, t)