2181. Merge Nodes in Between Zeros

Medium

You are given the head of a linked list, which contains a series of integers separated by 0's. The beginning and end of the linked list will have Node.val == 0.

For every two consecutive 0's, merge all the nodes lying in between them into a single node whose value is the sum of all the merged nodes. The modified list should not contain any 0's.

Return the head of the modified linked list.

Example 1:

Input: head = [0,3,1,0,4,5,2,0]
Output:
 [4,11]
Explanation:
 
The above figure represents the given linked list. The modified list contains
- The sum of the nodes marked in green: 3 + 1 = 4.
- The sum of the nodes marked in red: 4 + 5 + 2 = 11.

Example 2:

Input: head = [0,1,0,3,0,2,2,0]
Output:
 [1,3,4]
Explanation:
 
The above figure represents the given linked list. The modified list contains
- The sum of the nodes marked in green: 1 = 1.
- The sum of the nodes marked in red: 3 = 3.
- The sum of the nodes marked in yellow: 2 + 2 = 4.

Constraints:

• The number of nodes in the list is in the range [3, 2 * 105].

• 0 <= Node.val <= 1000

• There are no two consecutive nodes with Node.val == 0.

• The beginning and end of the linked list have Node.val == 0.

解題

Runtime: 332 ms, faster than 100%

Memory Usage: 15.2 MB, less than 84.69%

/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 */
func mergeNodes(head *ListNode) *ListNode {
    cur, pre := head.Next, head

    for cur.Next != nil {
        if cur.Val == 0 {
            pre.Next = cur
            pre = cur
        }
        pre.Val += cur.Val
        cur = cur.Next
    }

    pre.Next = nil

    return head
}