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1 | 1 | package LinkedList; |
2 | 2 |
|
| 3 | +import java.util.ArrayList; |
| 4 | +import java.util.Collections; |
| 5 | +import java.util.Comparator; |
| 6 | +import java.util.List; |
3 | 7 | import java.util.PriorityQueue; |
4 | 8 |
|
5 | 9 | public class MergeKSortedLists23 { |
@@ -44,4 +48,72 @@ public ListNode mergeKLists(ListNode[] lists) { |
44 | 48 | return dummy.next; |
45 | 49 | } |
46 | 50 |
|
| 51 | + // using arraylist and sorting |
| 52 | + // time O(NlogN) space O(N) |
| 53 | + public ListNode mergeKLists1(ListNode[] lists) { |
| 54 | + |
| 55 | + if (lists == null || lists.length == 0) |
| 56 | + return null; |
| 57 | + |
| 58 | + List<Integer> allnodes = new ArrayList<Integer>(); |
| 59 | + |
| 60 | + for (ListNode node : lists) { |
| 61 | + while (node != null) { |
| 62 | + allnodes.add(node.val); |
| 63 | + node = node.next; |
| 64 | + } |
| 65 | + } |
| 66 | + |
| 67 | + Collections.sort(allnodes); |
| 68 | + |
| 69 | + ListNode dummy = new ListNode(-1); |
| 70 | + ListNode tail = dummy; |
| 71 | + |
| 72 | + for (int value : allnodes) { |
| 73 | + tail.next = new ListNode(value); |
| 74 | + tail = tail.next; |
| 75 | + } |
| 76 | + |
| 77 | + return dummy.next; |
| 78 | + } |
| 79 | + |
| 80 | + // heap solution |
| 81 | + public ListNode mergeKLists2(ListNode[] lists) { |
| 82 | + |
| 83 | + PriorityQueue<ListNode> minheap = new PriorityQueue<ListNode>(lists.length, new Comparator<ListNode>() { |
| 84 | + @Override |
| 85 | + public int compare(ListNode l1, ListNode l2) { |
| 86 | + if (l1.val < l2.val) |
| 87 | + return -1; |
| 88 | + else if (l1.val > l2.val) |
| 89 | + return 1; |
| 90 | + else |
| 91 | + return 0; |
| 92 | + } |
| 93 | + }); |
| 94 | + |
| 95 | + |
| 96 | + // using java 8 |
| 97 | + |
| 98 | + // PriorityQueue<ListNode> minheap8 = new PriorityQueue<>(lists.length, (a,b) -> a.val - b.val); |
| 99 | + |
| 100 | + ListNode dummy = new ListNode(-1); |
| 101 | + ListNode tail = dummy; |
| 102 | + |
| 103 | + for (ListNode nodes : lists) { |
| 104 | + if (nodes != null) |
| 105 | + minheap.add(nodes); |
| 106 | + } |
| 107 | + |
| 108 | + while (!minheap.isEmpty()) { |
| 109 | + tail.next = minheap.poll(); |
| 110 | + tail = tail.next; |
| 111 | + |
| 112 | + if (tail.next != null) |
| 113 | + minheap.add(tail.next); |
| 114 | + } |
| 115 | + |
| 116 | + return dummy.next; |
| 117 | + } |
| 118 | + |
47 | 119 | } |
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