Lesson 2 arrays

jsueling · jsueling · commit 65cdd69fa05a · 2025-11-23T17:57:03.000Z
diff --git a/02_cyclic_rotation.py b/02_cyclic_rotation.py
@@ -0,0 +1,13 @@
+"""https://app.codility.com/programmers/lessons/2-arrays/cyclic_rotation/"""
+
+# Time complexity:
+# Slice array into two parts and concatenate them, each taking O(N) time per op
+# Overall = O(N)
+
+def solution(a: list[int], k: int) -> list[int]:
+    """Rotate array A to the right K times."""
+    n = len(a)
+    if n == 0:
+        return a
+    k = k % n  # if K is greater than N
+    return a[-k:] + a[:-k]
diff --git a/02_odd_occurrences_in_array.py b/02_odd_occurrences_in_array.py
@@ -0,0 +1,16 @@
+"""https://app.codility.com/programmers/lessons/2-arrays/odd_occurrences_in_array/"""
+
+# Time complexity:
+# Single pass through array, O(N)
+# XOR operation is O(log M) where M is the max value,
+# but M <= 1,000,000,000 is effectively constant (fits in 32/64 bits)
+# Overall = O(N)
+
+def solution(a: list[int]) -> int:
+    """Find the value that occurs in odd number of elements."""
+    result = 0
+    # XOR is commutative, associative and self-inverse.
+    # All pairs cancel, leaving the odd occurring number
+    for number in a:
+        result ^= number
+    return result
