reverseKGroupFromEnd

reverseKGroupFromEnd.js

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */
/**
 * @param {ListNode} head
 * @param {number} k
 * @return {ListNode}
 */
var reverseKGroup = function(head, k) {

    var l = (head => {
        var l = 0;
        while(head)
            head = head.next, l++;
        return l;
    })(head);
    
    var tail = {next:head};
    var result = tail;
    
    
    for(var j = 0; j < l % k; j ++)
        tail = tail.next;
    
    var groupHead = tail.next;
    for(var j = 0; j < (l - l % k)/k ; j++) {
        var last = null;
        var current = groupHead;
        var next = current.next;
        
        for(var i = 0; i < k; i++) {
            current.next = last;
            last = current;
            current = next;
            if(current)
                next = current.next;
        }
        tail.next = last;
        tail = groupHead;
        groupHead = current;
    }
    tail.next = groupHead;
    return result.next;
};