增加代码

Author: starsingchow

java/21.合并两个有序链表.java

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+/*
+ * @lc app=leetcode.cn id=21 lang=java
+ *
+ * [21] 合并两个有序链表
+ */
+
+// @lc code=start
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ *     int val;
+ *     ListNode next;
+ *     ListNode() {}
+ *     ListNode(int val) { this.val = val; }
+ *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
+ * }
+ */
+class Solution {
+    public ListNode mergeTwoLists(ListNode list1, ListNode list2) {
+        ListNode dummy = new ListNode();
+        ListNode curr = dummy;
+        while(list1 != null && list2 != null) {
+            if(list1.val < list2.val) {
+                curr.next = list1;
+                list1 = list1.next;
+            } else {
+                curr.next = list2;
+                list2 = list2.next;
+            }
+
+            curr = curr.next;
+        }
+
+        if(list1 != null) {
+            curr.next = list1;
+        }
+
+        if(list2 !=  null) {
+            curr.next = list2;
+        }
+
+        return dummy.next;
+    }
+}
+// @lc code=end
+

java/86.分隔链表.java

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+/*
+ * @lc app=leetcode.cn id=86 lang=java
+ *
+ * [86] 分隔链表
+ */
+
+// @lc code=start
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ *     int val;
+ *     ListNode next;
+ *     ListNode() {}
+ *     ListNode(int val) { this.val = val; }
+ *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
+ * }
+ */
+class Solution {
+    public ListNode partition(ListNode head, int x) {
+        if(head == null) return null;
+        ListNode node1 = new ListNode();
+        ListNode curr1 = node1;
+        ListNode node2 = new ListNode();
+        ListNode curr2 = node2;
+
+        while(head != null) {
+            if(head.val < x) {
+                curr1.next = head;
+                curr1 = curr1.next;
+            } else {
+                curr2.next = head;
+                curr2 = curr2.next;
+            }
+
+            head = head.next;
+        }
+
+        curr1.next = node2.next;
+        curr2.next = null;
+        return node1.next;
+    }
+}
+// @lc code=end
+

java/92.反转链表II.java

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+/*
+ * @lc app=leetcode.cn id=92 lang=java
+ *
+ * [92] 反转链表 II
+ */
+
+// @lc code=start
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ *     int val;
+ *     ListNode next;
+ *     ListNode() {}
+ *     ListNode(int val) { this.val = val; }
+ *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
+ * }
+ */
+class Solution {
+    public ListNode reverseBetween(ListNode head, int left, int right) {
+        if(head == null) {
+            return head;
+        }
+
+        ListNode dummy = new ListNode(0);
+        dummy.next = head;
+
+        ListNode pre = null;
+        int i = 1;
+        while(i < left) {
+            pre = head;
+            head = head.next;
+            i++;
+        }
+
+        int j = i;
+        ListNode next = null;
+        ListNode mid = head;
+        while(head != null && j <= right) {
+            ListNode temp = head.next;
+            head.next = next;
+            next = head;
+            head = temp;
+            j++;
+        }
+
+        if(pre != null) {
+            pre.next = next;
+        } else {
+            dummy.next = next;   
+        }
+        mid.next = head;
+        return dummy.next;
+    }
+}
+// @lc code=end
+