leetcode

commit ee22a93d9a3c5ed779e1ee3d440e887f33aef3d5
parent 5501e17242ca51209b6971c6f2ce413240775406
Author: Jack Sangdahl <jack@pngu.org>
Date:   Wed, 11 Feb 2026 21:34:38 -0700

189. rotate array

Diffstat:
A
rotate_array.c
 | 
40
++++++++++++++++++++++++++++++++++++++++
A
rotate_array.py
 | 
40
++++++++++++++++++++++++++++++++++++++++

2 files changed, 80 insertions(+), 0 deletions(-)
diff --git a/rotate_array.c b/rotate_array.c
@@ -0,0 +1,40 @@
+// 189. Rotate Array
+#include "leetcode.h"
+
+/*
+ * given an integer array 'nums', rotate the array to the right by 'k' stops,
+ * where 'k' is non-negative.
+ */
+
+void reverse(int *nums, int start, int end) {
+  while (start < end) {
+    nums[start] ^= nums[end];
+    nums[end] ^= nums[start];
+    nums[start++] ^= nums[end--];
+  }
+}
+
+void rotate(int *nums, int numsSize, int k) {
+  int start = 0, end = numsSize - 1;
+  k %= numsSize;
+  reverse(nums, start, end - k);
+  reverse(nums, numsSize - k, end);
+  reverse(nums, start, end);
+}
+
+int main() {
+  int n1[] = {1, 2, 3, 4, 5, 6, 7}, r1[] = {5, 6, 7, 1, 2, 3, 4};
+  int n2[] = {-1, -100, 3, 99}, r2[] = {3, 99, -1, -100};
+  rotate(n1, ARRAY_SIZE(n1), 3);
+  rotate(n2, ARRAY_SIZE(n2), 2);
+  for (int i = 0; i < ARRAY_SIZE(n1); i++) {
+    printf("%d ", n1[i]);
+    assert(r1[i] == n1[i]);
+  }
+  printf("\n");
+  for (int i = 0; i < ARRAY_SIZE(n2); i++) {
+    printf("%d ", n2[i]);
+    assert(r2[i] == n2[i]);
+  }
+  printf("\n");
+}
diff --git a/rotate_array.py b/rotate_array.py
@@ -0,0 +1,40 @@
+# 189. Rotate Array
+
+"""
+given an integer array 'nums', rotate the array to the right by 'k' stops,
+where 'k' is non-negative.
+"""
+
+
+class Solution(object):
+    def reverse(self, nums, start, end):
+        while start < end:
+            tmp = nums[start]
+            nums[start] = nums[end]
+            nums[end] = tmp
+            start += 1
+            end -= 1
+
+    def rotate(self, nums, k):
+        """
+        :type nums: List[int]
+        :type k: int
+        :rtype: None Do not return anything, modify nums in-place instead.
+        """
+        n = len(nums)
+        k %= n
+        if k < 0:
+            k += n
+        self.reverse(nums, 0, n - k - 1)
+        self.reverse(nums, n - k, n - 1)
+        self.reverse(nums, 0, n - 1)
+
+
+if __name__ == "__main__":
+    obj = Solution()
+    n1 = [1, 2, 3, 4, 5, 6, 7]
+    n2 = [-1, -100, 3, 99]
+    obj.rotate(n1, k=3)
+    obj.rotate(n2, k=2)
+    print(n1)
+    print(n2)