[Function add]

1. Add leetcode solutions with tag list.

Author: Seanforfun

leetcode/148. Sort List.md

@@ -115,4 +115,52 @@ class Solution {
         return dummy.next;
     }
 }
-```
+```
+
+### Third Time
+* Method 1: Divide and conquer
+	```Java
+	/**
+	 * Definition for singly-linked list.
+	 * public class ListNode {
+	 *     int val;
+	 *     ListNode next;
+	 *     ListNode(int x) { val = x; }
+	 * }
+	 */
+	class Solution {
+		public ListNode sortList(ListNode head) {
+			if(head == null || head.next == null) return head;
+			ListNode dummy = new ListNode(0);
+			dummy.next = head;
+			ListNode slow = dummy, fast = dummy;
+			while(fast != null && fast.next != null){
+				slow = slow.next;
+				fast = fast.next.next;
+			}
+			ListNode second = slow.next;
+			slow.next = null;
+			ListNode l1 = sortList(head);
+			ListNode l2 = sortList(second);
+			return merge(l1, l2);
+		}
+		private ListNode merge(ListNode l1, ListNode l2){        
+			ListNode dummy = new ListNode(0), cur = dummy;
+			while(l1 != null || l2 != null){
+				if(l1 != null && l2 != null){
+					cur.next = l1.val <= l2.val ? l1: l2;
+					if(l1.val <= l2.val) l1 = l1.next;
+					else l2 = l2.next;
+				}else if(l1 != null){
+					cur.next = l1;
+					break;
+				}else{
+					cur.next = l2;
+					break;
+				}
+				cur = cur.next;
+			}
+			return dummy.next;
+		}
+	}
+	```

leetcode/21. Merge Two Sorted Lists.md

@@ -79,3 +79,36 @@ class Solution {
     }
 }
 ```
+
+### Third Time
+* Method 1: Basic list question
+	```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) {
+			ListNode dummy = new ListNode(0), cur = dummy;
+			while(l1 != null || l2 != null){
+				if(l1 != null && l2 != null){
+					cur.next = l1.val < l2.val ? l1: l2;
+					if(l1.val < l2.val) l1 = l1.next;
+					else l2 = l2.next;
+				}else if(l1 != null){
+					cur.next = l1;
+					l1 = l1.next;
+				}else{
+					cur.next = l2;
+					l2 = l2.next;
+				}
+				cur = cur.next;
+			}
+			return dummy.next;
+		}
+	}
+	```

leetcode/23. Merge k Sorted Lists.md

@@ -128,4 +128,52 @@ class Solution {
         return dummy.next;
     }
 }
-```
+```
+
+### Third Time
+* Method 1: Divide and conqur
+	```Java
+	/**
+	 * Definition for singly-linked list.
+	 * public class ListNode {
+	 *     int val;
+	 *     ListNode next;
+	 *     ListNode(int x) { val = x; }
+	 * }
+	 */
+	class Solution {
+		private ListNode[] l;
+		public ListNode mergeKLists(ListNode[] lists) {
+			if(lists.length == 0) return null;
+			else if(lists.length == 1) return lists[0];
+			this.l = lists;
+			return sort(0, this.l.length - 1);
+		}
+		private ListNode sort(int low, int high){
+			if(low >= high) return l[low];
+			int mid = low + (high - low) / 2;
+			ListNode l1 = sort(low, mid);
+			ListNode l2 = sort(mid + 1, high);
+			return merge(l1, l2);
+		}
+		private ListNode merge(ListNode l1, ListNode l2){
+			ListNode dummy = new ListNode(0), cur = dummy;
+			ListNode first = l1, second = l2;
+			while(first != null || second != null){
+				if(first != null && second != null){
+					cur.next = first.val < second.val ? first: second;
+					if(first.val < second.val) first = first.next;
+					else second = second.next;
+				}else if(first != null){
+					cur.next = first;
+					break;
+				}else{
+					cur.next = second;
+					break;
+				}
+				cur = cur.next;
+			}
+			return dummy.next;
+		}
+	}
+	```