25. K 个一组翻转链表

题解

/**
 * Definition for singly-linked list.
 * function ListNode(val, next) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.next = (next===undefined ? null : next)
 * }
 */
/**
 * @param {ListNode} head
 * @param {number} k
 * @return {ListNode}
 */
const reverse = (head, b) => {
    if (!head) return null;
    let target = head;
    let pre = null;
    while (target != b) {
        let temp = target.next;
        target.next = pre;
        pre = target;
        target = temp;
    }
    return pre;
}
var reverseKGroup = function (head, k) {
    if (!head) return null;
    let a = b = head;
    for (let i = 0; i < k; i++) {
        if (!b) return head;
        b = b.next;
    }
    let newNode = reverse(a, b);
    a.next = reverseKGroup(b, k);
    return newNode;
};