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Code04_ReverseNodesInKGroup.java
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57 lines (51 loc) · 1.2 KB
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package class04;
// 测试链接：https://leetcode.com/problems/reverse-nodes-in-k-group/
public class Code04_ReverseNodesInKGroup {
// 不要提交这个类
public static class ListNode {
public int val;
public ListNode next;
}
public static ListNode reverseKGroup(ListNode head, int k) {
ListNode start = head;
ListNode end = getKGroupEnd(start, k);
if (end == null) {
return head;
}
// 第一组凑齐了！
head = end;
reverse(start, end);
// 上一组的结尾节点
ListNode lastEnd = start;
while (lastEnd.next != null) {
start = lastEnd.next;
end = getKGroupEnd(start, k);
if (end == null) {
return head;
}
reverse(start, end);
lastEnd.next = end;
lastEnd = start;
}
return head;
}
public static ListNode getKGroupEnd(ListNode start, int k) {
while (--k != 0 && start != null) {
start = start.next;
}
return start;
}
public static void reverse(ListNode start, ListNode end) {
end = end.next;
ListNode pre = null;
ListNode cur = start;
ListNode next = null;
while (cur != end) {
next = cur.next;
cur.next = pre;
pre = cur;
cur = next;
}
start.next = end;
}
}