solution for: Sort List with merge sort

Author: edyluisrey

src/leetcode/SortListTest.java

@@ -0,0 +1,60 @@
+package leetcode;
+
+public class SortListTest {
+
+	public static void main(String[] args) {
+		SortListTest test = new SortListTest();
+		ListNode l = new ListNode(4);
+	    l.next =  new ListNode(3);
+	    l.next.next = new ListNode(1);
+	    ListNode re= test.sortList(l);
+		System.out.println(re.val);
+	}
+	
+	public ListNode sortList(ListNode head) {
+	    if(head ==null || head.next==null)  return head;  
+	    ListNode fast = head;
+	    ListNode slow = head;
+	    ListNode prev= null;
+	    while(fast!=null && fast.next!=null){
+	    	prev=slow;
+	    	fast= fast.next.next;
+	    	slow= slow.next;
+	    }
+	    prev.next=null;
+	    ListNode l1 = sortList(head);
+	    ListNode l2 = sortList(slow);
+	    return merge(l1,l2);
+	}
+	
+	public ListNode merge(ListNode l1, ListNode l2){
+		ListNode result = new ListNode(0);
+		ListNode l= result;
+		while(l1!=null && l2!=null){
+			if(l1.val < l2.val){
+				l.next = l1;
+				l1= l1.next;
+			}		
+			else{
+				l.next = l2;
+				l2= l2.next;
+			}	
+			l= l.next;
+		}
+		
+		if(l1!=null)
+			l.next= l1;
+		if(l2!=null)
+			l.next = l2;
+		return result.next;
+	}
+		
+}
+
+class ListNode{
+	int val;
+	ListNode next;
+	ListNode(int x){
+		val=x;
+	}
+}