leetcode

commit a4decacf501f8189aede3358a641fab291dfd7ce
parent 48092c680db162869b6a39e8e372bbb0f1bfb399
Author: Jack Sangdahl <jack@pngu.org>
Date:   Mon,  4 May 2026 21:31:10 -0600

61. rotate list

Diffstat:
M
leetcode.c
 | 
5
++++-
M
leetcode.h
 | 
2
+-
A
rotate_list.c
 | 
37
+++++++++++++++++++++++++++++++++++++
A
rotate_list.py
 | 
36
++++++++++++++++++++++++++++++++++++

4 files changed, 78 insertions(+), 2 deletions(-)
diff --git a/leetcode.c b/leetcode.c
@@ -39,11 +39,14 @@ struct ListNode *listnode_build(int *vals, int size) {
   return head;
 }
 
-void listnode_print(struct ListNode *head) {
+void listnode_print(struct ListNode *head, int *expected) {
   struct ListNode *curr = head;
+  int n = 0;
   while (curr != NULL) {
     printf("%d ", curr->val);
+    assert(curr->val == expected[n]);
     curr = curr->next;
+    n++;
   }
   printf("\n");
 }
diff --git a/leetcode.h b/leetcode.h
@@ -41,7 +41,7 @@ void two_d_arr_free(struct two_d_arr *obj);
 
 struct ListNode *listnode_create(int val);
 struct ListNode *listnode_build(int *vals, int size);
-void listnode_print(struct ListNode *head);
+void listnode_print(struct ListNode *head, int *expected);
 void listnode_free(struct ListNode *head);
 
 struct TreeNode *treenode_create(int val);
diff --git a/rotate_list.c b/rotate_list.c
@@ -0,0 +1,37 @@
+// 61. Rotate List
+#include "leetcode.h"
+
+/*
+ * given the 'head' of a linked list, rotate the list to the rigt by 'k' places.
+ */
+
+struct ListNode *rotateRight(struct ListNode *head, int k) {
+  if (!head)
+    return NULL;
+  int n = 1;
+  struct ListNode *tail = head;
+  while (tail->next) {
+    n++;
+    tail = tail->next;
+  }
+  tail->next = head;
+  int m = n - k % n;
+  for (int i = 0; i < m; i++)
+    tail = tail->next;
+  head = tail->next;
+  tail->next = NULL;
+  return head;
+}
+
+int main() {
+  int h1i[] = {1, 2, 3, 4, 5}, r1[] = {4, 5, 1, 2, 3};
+  int h2i[] = {0, 1, 2}, r2[] = {2, 0, 1};
+  struct ListNode *h1 = listnode_build(h1i, ARRAY_SIZE(h1i));
+  struct ListNode *h2 = listnode_build(h2i, ARRAY_SIZE(h2i));
+  struct ListNode *rr1 = rotateRight(h1, 2);
+  struct ListNode *rr2 = rotateRight(h2, 4);
+  listnode_print(rr1, r1);
+  listnode_print(rr2, r2);
+  listnode_free(h1);
+  listnode_free(h2);
+}
diff --git a/rotate_list.py b/rotate_list.py
@@ -0,0 +1,36 @@
+# 61. Rotate List
+from typing import Optional
+
+from leetcode import ListNode, listnode_build
+
+"""
+given the 'head' of a linked list, rotate the list to the rigt by 'k' places.
+"""
+
+
+class Solution:
+    def rotateRight(self, head: Optional[ListNode], k: int) -> Optional[ListNode]:
+        if not head or not head.next:
+            return head
+        curr = head
+        len = 1
+        while curr.next:
+            curr = curr.next
+            len += 1
+        curr.next = head
+        k = k % len
+        print(k)
+        print(len)
+        for i in range(len - k):
+            curr = curr.next
+        head = curr.next
+        curr.next = None
+        return head
+
+
+if __name__ == "__main__":
+    obj = Solution()
+    h1 = listnode_build(vals=[1, 2, 3, 4, 5])
+    h2 = listnode_build(vals=[0, 1, 2])
+    print(obj.rotateRight(h1, k=2))
+    print(obj.rotateRight(h1, k=4))