21. Merge Two Sorted Lists

Author: coderbean

src/leetcode/_0_template/Main.java

@@ -1,7 +1,5 @@
 package leetcode._0_template;
 
-import leetcode._19_.ListNode;
-
 /**
  * Created by zhangbo54 on 2019-03-04.
  */

src/leetcode/_19_/Main.java

@@ -1,5 +1,7 @@
 package leetcode._19_;
 
+import leetcode.common.ListNode;
+
 /**
  * Created by zhangbo54 on 2019-03-04.
  */

src/leetcode/_19_/Solution.java

@@ -1,11 +1,6 @@
 package leetcode._19_;
 
-import java.util.ArrayList;
-import java.util.Arrays;
-import java.util.Collections;
-import java.util.HashSet;
-import java.util.List;
-import java.util.Set;
+import leetcode.common.ListNode;
 
 /**
  * Definition for singly-linked list.

src/leetcode/_21_/Main.java

@@ -0,0 +1,16 @@
+package leetcode._21_;
+
+import leetcode.common.ListNode;
+
+/**
+ * Created by zhangbo54 on 2019-03-04.
+ */
+public class Main {
+    public static void main(String[] args) {
+        Solution solution = new Solution();
+        ListNode node = new ListNode(1).setNext(new ListNode(2).setNext(new ListNode(4)));
+        ListNode node2 = new ListNode(1).setNext(new ListNode(3).setNext(new ListNode(4)));
+        System.out.println(solution.mergeTwoLists(node, node2));
+    }
+}
+

src/leetcode/_21_/Solution.java

@@ -0,0 +1,49 @@
+package leetcode._21_;
+
+import leetcode.common.ListNode;
+
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ * int val;
+ * ListNode next;
+ * ListNode(int x) { val = x; }
+ * }
+ */
+class Solution {
+    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
+        if (l1 == null) {
+            return l2;
+        }
+        if (l2 == null) {
+            return l1;
+        }
+        int headVal = 0;
+        if (l1.val > l2.val) {
+            headVal = l2.val;
+            l2 = l2.next;
+        } else {
+            headVal = l1.val;
+            l1 = l1.next;
+        }
+        ListNode head = new ListNode(headVal);
+        ListNode index = head;
+        while (l1 != null && l2 != null) {
+            if (l1.val > l2.val) {
+                index.next = new ListNode(l2.val);
+                l2 = l2.next;
+            } else {
+                index.next = new ListNode(l1.val);
+                l1 = l1.next;
+            }
+            index = index.next;
+        }
+        if (l1 != null) {
+            index.next = l1;
+        }
+        if (l2 != null) {
+            index.next = l2;
+        }
+        return head;
+    }
+}

src/leetcode/_21_/solution.md

@@ -0,0 +1,68 @@
+### [21\. Merge Two Sorted Lists](https://leetcode.com/problems/merge-two-sorted-lists/)
+
+Difficulty: **Easy**
+
+
+Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.
+
+**Example:**
+
+```
+Input: 1->2->4, 1->3->4
+Output: 1->1->2->3->4->4
+```
+
+
+#### Solution
+
+Language: **Java**
+
+```java
+​
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ * int val;
+ * ListNode next;
+ * ListNode(int x) { val = x; }
+ * }
+ */
+class Solution {
+    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
+        if (l1 == null) {
+            return l2;
+        }
+        if (l2 == null) {
+            return l1;
+        }
+        int headVal = 0;
+        if (l1.val > l2.val) {
+            headVal = l2.val;
+            l2 = l2.next;
+        } else {
+            headVal = l1.val;
+            l1 = l1.next;
+        }
+        ListNode head = new ListNode(headVal);
+        ListNode index = head;
+        while (l1 != null && l2 != null) {
+            if (l1.val > l2.val) {
+                index.next = new ListNode(l2.val);
+                l2 = l2.next;
+            } else {
+                index.next = new ListNode(l1.val);
+                l1 = l1.next;
+            }
+            index = index.next;
+        }
+        if (l1 != null) {
+            index.next = l1;
+        }
+        if (l2 != null) {
+            index.next = l2;
+        }
+        return head;
+    }
+}
+```
+![](https://ws4.sinaimg.cn/large/006tKfTcgy1g0ui2op9ucj31180scgpp.jpg)

src/leetcode/_19_/ListNode.java renamed to src/leetcode/common/ListNode.java

@@ -1,28 +1,16 @@
-package leetcode._19_;
+package leetcode.common;
 
 /**
  * Created by zhangbo54 on 2019-03-06.
  */
 public class ListNode {
-    int val;
-    ListNode next;
+    public int val;
+    public ListNode next;
 
-    ListNode(int x) {
+    public ListNode(int x) {
         val = x;
     }
 
-    public int getVal() {
-        return val;
-    }
-
-    public void setVal(int val) {
-        this.val = val;
-    }
-
-    public ListNode getNext() {
-        return next;
-    }
-
     public ListNode setNext(ListNode next) {
         this.next = next;
         return this;