24

suke · suke · commit f7deb238745b · 2019-05-06T15:46:09.000+08:00
diff --git a/Week_01/id_121/LeetCode_24_121.java b/Week_01/id_121/LeetCode_24_121.java
@@ -0,0 +1,46 @@
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ *     int val;
+ *     ListNode next;
+ *     ListNode(int x) { val = x; }
+ * }
+ */
+class Solution {
+    public ListNode swapPairs(ListNode head) {
+        if(head == null ){
+            return null;
+        }
+        if(head.next == null){
+            return head;
+        }
+
+        ListNode preNode = head;
+        ListNode curNode = head.next;
+        ListNode retNode = curNode;
+        ListNode newPreNode = null;
+        while(preNode != null && curNode != null){
+            removeCurNode(preNode,curNode);
+            insertBeforeCurNode(newPreNode,preNode,curNode);
+            preNode = curNode.next.next;
+            newPreNode = curNode.next;
+            if(preNode != null){
+                curNode = preNode.next;
+            }
+        }
+        return retNode;
+    }
+
+    private void removeCurNode(ListNode preNode,ListNode curNode){
+        if(preNode != null){
+            preNode.next = curNode.next;
+        }
+        curNode.next = null;
+    }
+    private void insertBeforeCurNode(ListNode preNode,ListNode curNode,ListNode node){
+        node.next = curNode;
+        if(preNode != null){
+            preNode.next = node;
+        }
+    }
+}
