[Leetcode] 25. Reverse Nodes in k-Group

/**
 * 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}
 */
var reverseKGroup = function(head, k) {
    
    const preHead = new ListNode(0,head)
    let rear = preHead
    
    const reverseNode = (node) => {
        let mvNode = node
        let start = new ListNode()
        let end = null
        let pointer = start
        let arr = []
        
        for(let i = 0 ; i < k ; i++) {
            if (!mvNode) return node
            if (i === k-1) end = mvNode.next
            arr.push({...mvNode})
            mvNode = mvNode.next
        }
        
        arr.reverse().forEach(item => {
            if(!start.next) start.next = item
            pointer.next = item
            pointer = pointer.next
        })
        
        pointer.next = end
        
        return start.next
    }
    
    while(rear) {
        
        const temp = reverseNode(rear.next)
        // console.log(temp)
        if (!preHead.next) preHead.next = temp
        rear.next = temp
        for(let i = 0 ; i < k ; i++) {
            if (!rear) break
            rear = rear.next
        }
    }
    
    return preHead.next
};