ReverseNodesKGroup
ReverseNodesKGroup.java 源码
package datastructure.linkedlist.leetcode;
import java.util.ArrayList;
import java.util.List;
/**
* @author roseduan
* @time 2021/1/2 12:04 上午
* @description k个一组翻转链表
*/
public class ReverseNodesKGroup {
/**
* 比较易于理解的暴力法
* 先将链表数据存储到数组中，再反转，然后构建新的链表
*/
public ListNode reverseKGroup1(ListNode head, int k) {
if (k <= 1) {
return head;
}
List<Integer> list = new ArrayList<>();
while (head != null) {
list.add(head.val);
head = head.next;
}
Integer[] array = list.toArray(new Integer[]{});
int step = 0;
while (step + k <= array.length) {
reverseArr(step, step + k - 1, array);
step += k;
}
ListNode dummy = new ListNode(-1);
ListNode p = dummy;
for (Integer integer : array) {
p.next = new ListNode(integer);
p = p.next;
}
return dummy.next;
}
private void reverseArr(int x, int y, Integer[] arr){
for (int i = x, j = y; i < j; i++, j--) {
int temp = arr[i];
arr[i] = arr[j];
arr[j] = temp;
}
}
/**
* 官方解法
*/
public ListNode reverseKGroup2(ListNode head, int k) {
ListNode dummy = new ListNode(-1);
dummy.next = head;
ListNode prev = dummy, end = dummy;
while (end.next != null) {
for (int i = 0; i < k && end != null; i++) {
end = end.next;
}
if (end == null) {
break;
}
ListNode start = prev.next, next = end.next;
end.next = null;
prev.next = reverseList(start);
start.next = next;
prev = end = start;
}
return dummy.next;
}
private ListNode reverseList(ListNode head) {
ListNode prev = null, p = head;
while (p != null) {
ListNode next = p.next;
p.next = prev;
prev = p;
p = next;
}
return prev;
}
private static class ListNode {
int val;
ListNode next;
ListNode(int x) { val = x; }
}
}
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