Reverse K-group Node

Let’s continue the last problem. Here is the question I don’t understanind last time.

1. How does the dummy.next change? Accurately When did the dummy.next change?

   Here is the answer.(How does the dummy.next change?)[https://leetcode.com/problems/reverse-nodes-in-k-group/discuss/11491/Succinct-iterative-Python-O(n)-time-O(1)-space/168139] This is related about how the python assign the variable. It’s pretty hard to understand for people first time.

2. How the program connect two K-group?

   Let’s tear jump.next, jump, l = pre, l, r apart.

   jump.next = pre # this line just do the dummy.next work in the first iteration, second iteartion this line link the previou KGroup tail and next KGroup head, this is the part someone really confused about.
   jump.next, jump = prev, l # connect the prev K-group an next K-group
   l = r # move the K-group boundary
   

Let’s take a look again.

class Solution(object):
    def reverseKGroup(self, head, k):
        dummy = jump = ListNode(0)
        dummy.next = l = r = head

        while True:
            count = 0
            while r and count < k:
                r = r.next
                count += 1
            if count == k:
                pre, cur = r, l
                for _ in range(k):
                    cur.next, cur, pre = pre, cur.next, cur
                jump.next, jump, l = pre, l, r
            else:
                return dummy.next

Follwing is my draft about this problem Haha.

Hope you guys can understand this one.

Conclusion

这道题看了一天，最终还是看懂了，有些感悟写在下面

Someone born with a silver spoon in the mouth, someone not, the only thing you can do is accept that, and moving on your fuking way, there must be something great waiting for you, maybe a fuking gold mine.