Create Sort_List.cc

Author: iphkwan

Sort_List.cc

@@ -0,0 +1,47 @@
+/**
+ * Definition for singly-linked list.
+ * struct ListNode {
+ *     int val;
+ *     ListNode *next;
+ *     ListNode(int x) : val(x), next(NULL) {}
+ * };
+ */
+class Solution {
+public:
+    ListNode *sortList(ListNode *head) {
+        // IMPORTANT: Please reset any member data you declared, as
+        // the same Solution instance will be reused for each test case.
+        if (!head || !head->next)
+            return head;
+        ListNode *fast = head, *slow = head, *tmp = NULL;
+        
+        //split
+        while (fast && fast->next) {
+            fast = fast->next->next;
+            tmp = slow;
+            slow = slow->next;
+        }
+        tmp->next = NULL;
+        
+        //recursion
+        head = sortList(head);
+        slow = sortList(slow);
+        
+        //merge
+        ListNode *ret = NULL;
+        ListNode **pCur = &ret;
+        while (head && slow) {
+            if (head->val <= slow->val) {
+                *pCur = head;
+                head = head->next;
+            } else {
+                *pCur = slow;
+                slow = slow->next;
+            }
+            pCur = &((*pCur)->next);
+        }
+        if (head)   *pCur = head;
+        if (slow)    *pCur = slow;
+        return ret;
+    }
+};