K 个一组翻转链表

K 个一组翻转链表

1. 新建一个head前面的hair节点

   var reverseKGroup = function (head, k) {
     const hair = new ListNode(-1, head);
   };
   

   2. 从head开始k个翻转, 注意此时会先遍历从开始是否有k个节点

   var reverseKGroup = function (head, k) {
     const hair = new ListNode(-1, head);
     let cur = hair;
     cur.next = reverse(cur.next, k);
   };
   function reverse(head, k) {
     let count = k;
     let cur = head;
     while (--count && cur) {
       cur = cur.next;
     }
     // 表示从 head 开始没有 k 个节点
     if (!cur) return head;
     // 至少有k个节点
     cur = head;
     let prev = null;
     while (k--) {
       const next = head.next;
       cur.next = prev;
       prev = cur;
       cur = next;
     }
     head.next = cur;
     return prev;
   }
   

   3. 上述是开始翻转了head的k个节点，那么需要继续找到head之后的第k个节点继续翻转

   var reverseKGroup = function (head, k) {
     const hair = new ListNode(-1, head);
     let cur = hair;
     // 为的是一直遍历
     do {
       cur.next = reverse(cur.next, k);
       for (let i = 0; i < k && cur; i++) {
         cur = cur.next;
       }
       if (!cur) return hair.next;
     } while (true);
   };
   function reverse(head, k) {
     let count = k;
     let cur = head;
     while (--count && cur) {
       cur = cur.next;
     }
     // 表示从 head 开始没有 k 个节点
     if (!cur) return head;
     // 至少有k个节点
     cur = head;
     let prev = null;
     while (k--) {
       const next = head.next;
       cur.next = prev;
       prev = cur;
       cur = next;
     }
     head.next = cur;
     return prev;
   }