Merge pull request neetcode-gh#1603 from javiermon/148-Sort-List

C Solution to Neetcode: 148 SortList

c/0148-Sort-List.c

@@ -0,0 +1,70 @@
+/**
+ * Definition for singly-linked list.
+ * struct ListNode {
+ * int val;
+ * struct ListNode *next;
+ * };
+ */
+
+struct ListNode* merge(struct ListNode *list1, struct ListNode *list2) {
+ struct ListNode *head, *tail;
+
+ if (!list1 || !list2) {
+ if (!list1) {
+ return list2;
+ }
+ return list1;
+ }
+
+ if (list1->val < list2->val) {
+ head = list1;
+ list1 = list1->next;
+ } else {
+ head = list2;
+ list2 = list2->next;
+ }
+ tail = head;
+
+ while (list1 && list2) {
+ if (list1->val < list2->val) {
+ tail->next = list1;
+ list1 = list1->next;
+ } else {
+ tail->next = list2;
+ list2 = list2->next;
+ }
+ tail = tail->next;
+ }
+
+ if (list1) {
+ tail->next = list1;
+ }
+
+ if (list2) {
+ tail->next = list2;
+ }
+
+ return head;
+}
+
+// Split a linked list in two halfs:
+struct ListNode* split(struct ListNode* head) {
+ struct ListNode *slow = head, *fast = head, *prev = NULL;
+
+ while (fast && fast->next) {
+ prev = slow;
+ slow = slow->next;
+ fast = fast->next->next;
+ }
+
+ prev->next = NULL;
+ return slow;
+}
+
+struct ListNode* sortList(struct ListNode *head) {
+ if (!head || !head->next) {
+ return head;
+ }
+
+ return merge(sortList(head), sortList(split(head)));
+}