Create Recorder_List.cc

split, reverse and cross-merge

Author: iphkwan

Recorder_List.cc

@@ -0,0 +1,55 @@
+/**
+ * Definition for singly-linked list.
+ * struct ListNode {
+ *     int val;
+ *     ListNode *next;
+ *     ListNode(int x) : val(x), next(NULL) {}
+ * };
+ */
+class Solution {
+public:
+    void reorderList(ListNode *head) {
+        // IMPORTANT: Please reset any member data you declared, as
+        // the same Solution instance will be reused for each test case.
+        head = mergeList(head, reverseList(splitList(head)));
+        return;
+    }
+private:
+    ListNode *splitList(ListNode * head) {
+        if (!head)
+            return NULL;
+        ListNode *fast = head, *slow = head;
+        while (fast && fast->next) {
+            fast = fast->next->next;
+            slow = slow->next;
+        }
+        fast = slow->next;
+        slow->next = NULL;
+        return fast;
+    }
+    ListNode *reverseList(ListNode *head) {
+        ListNode *pre = NULL, *cur = head, *nxt = NULL;
+        while (cur) {
+            nxt = cur->next;
+            cur->next = pre;
+            pre = cur;
+            cur = nxt;
+        }
+        return pre;
+    }
+    ListNode *mergeList(ListNode *ha, ListNode *hb) {
+        ListNode *ret = NULL;
+        ListNode **pCur = &ret;
+        while (ha && hb) {
+            *pCur = ha;
+            pCur = &(ha->next);
+            ha = ha->next;
+            
+            *pCur = hb;
+            pCur = &(hb->next);
+            hb = hb->next;
+        }
+        *pCur = ha;
+        return ret;
+    }
+};