general: ex4: add solution

general/ex4.py

@@ -0,0 +1,19 @@
+#!/usr/bin/env python
+
+
+def naive_solution(x: int) -> int:
+    assert 0 <= x < 10, f"{x} is not a digit"
+    xx = x * 10 + x
+    xxx = xx * 10 + x
+    xxxx = xxx * 10 + x
+    return x + xx + xxx + xxxx
+
+
+def solution(x: int) -> int:
+    assert 0 <= x < 10, f"{x} is not a digit"
+    return x * 1234
+
+
+if __name__ == "__main__":
+    for x in range(10):
+        print(f"{naive_solution(x)} == {solution(x)}")