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LeetCode23.java
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72 lines (67 loc) · 1.99 KB
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package problems;
public class LeetCode23 {
public ListNode mergeKLists(ListNode[] lists) {
int n = lists.length;
return mergeSort(lists, 0, n - 1);
}
private ListNode mergeSort(ListNode[] lists, int left, int right) {
if (left == right) {
return lists[left];
}
if (left > right) {
return null;
}
int mid = (left + right) / 2;
return mergeTwoLists(mergeSort(lists, left, mid), mergeSort(lists, mid + 1, right));
}
private ListNode mergeTwoLists(ListNode a, ListNode b) {
if (a == null || b == null) {
return a != null ? a : b;
}
ListNode head = new ListNode(0);
ListNode tail = head, aPtr = a, bPtr = b;
while (aPtr != null && bPtr != null) {
if (aPtr.val < bPtr.val) {
tail.next = aPtr;
aPtr = aPtr.next;
} else {
tail.next = bPtr;
bPtr = bPtr.next;
}
tail = tail.next;
}
tail.next = (aPtr != null ? aPtr : bPtr);
return head.next;
}
}
/**
* 简单解法：顺序合并
*/
class LeetCode23_1 {
public ListNode mergeKLists(ListNode[] lists) {
ListNode ans = null;
for (int i = 0; i < lists.length; i++) {
ans = mergeTwoLists(ans, lists[i]);
}
return ans;
}
private ListNode mergeTwoLists(ListNode a, ListNode b) {
if(a == null || b == null) {
return a != null ? a:b;
}
ListNode dummyNode = new ListNode(0);
ListNode ptr = dummyNode, aPtr = a, bPtr = b;
while (aPtr != null && bPtr != null) {
if(aPtr.val < bPtr.val) {
ptr.next = aPtr;
aPtr = aPtr.next;
} else {
ptr.next = bPtr;
bPtr = bPtr.next;
}
ptr = ptr.next;
}
ptr.next = (aPtr != null ? aPtr : bPtr);
return dummyNode.next;
}
}