Merge pull request #173 from niranjana687/patch-3

Create MergeKSortedLists.java

Author: SarthakKeshari

LeetCode/MergeKSortedLists.java

@@ -0,0 +1,45 @@
+//Solution to https://leetcode.com/problems/merge-k-sorted-lists/
+//Approach: We use the logic behind merging two sorted lists to merge k number of lists in sorted order. 
+//Pair up k lists and merge each pair.
+//After the first pairing, k lists are merged into k/2 lists with average 2N/k length, then k/4, k/8 and so on.
+//This is repeated until we get the final sorted linked list.
+
+class Solution {
+    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
+    ListNode h = new ListNode(0);
+    ListNode ans=h;
+    while (l1 != null && l2 != null) {
+        if (l1.val < l2.val) {
+            h.next = l1;
+            h = h.next;
+            l1 = l1.next;
+        } else {
+            h.next = l2;
+            h = h.next;
+            l2 = l2.next;
+        }
+    }
+    if(l1==null){
+        h.next=l2;
+    }
+    if(l2==null){
+        h.next=l1;
+    } 
+    return ans.next;
+}
+public ListNode mergeKLists(ListNode[] lists) {
+    if(lists.length==0){
+        return null;
+    }
+    int interval = 1;
+    while(interval<lists.length){
+        System.out.println(lists.length);
+        for (int i = 0; i + interval< lists.length; i=i+interval*2) {
+            lists[i]=mergeTwoLists(lists[i],lists[i+interval]);            
+        }
+        interval*=2;
+    }
+
+    return lists[0];
+}
+}