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mergeKSorted.java
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mergeKSorted.java
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import java.util.*;
public class mergeKSorted {
private class ListNode {
int val;
ListNode next;
ListNode(int x) {
val = x;
next = null;
}
}
private ListNode merge2Lists(ListNode l1, ListNode l2) {
ListNode mergedHead = new ListNode(-1);
ListNode mergedCurr = mergedHead;
while(true) {
if (l1 == null && l2 == null) break;
else if (l1 == null) {
mergedCurr.next = l2;
l2 = l2.next;
mergedCurr = mergedCurr.next;
}
else if (l2 == null) {
mergedCurr.next = l1;
l1 = l1.next;
mergedCurr = mergedCurr.next;
}
else if (l1.val < l2.val) {
mergedCurr.next = l1;
l1 = l1.next;
mergedCurr = mergedCurr.next;
}
else {
mergedCurr.next = l2;
l2 = l2.next;
mergedCurr = mergedCurr.next;
}
}
return mergedHead.next;
}
public ListNode mergeKLists(List<ListNode> lists) {
int N = lists.size();
if (N == 0) return null;
if (N == 1) return lists.get(0);
if (N == 2) return merge2Lists(lists.get(0), lists.get(1));
ArrayList temp = new ArrayList<ListNode>();
for (int i = 0; i < N / 2; i++) {
temp.add(merge2Lists(lists.get(2 * i), lists.get(2 * i + 1)));
}
if (N % 2 == 1) {
temp.add(lists.get(N - 1));
}
return mergeKLists(temp);
}
}