LeetCode -- Reverse Nodes in k-Group

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     public int val;
 *     public ListNode next;
 *     public ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ListNode ReverseKGroup(ListNode head, int k) 
    {
        if(head == null || head.next == null || k == 1){
    		return head;
    	}
    	
    	var len = 0;
    	var h = head;
    	while(head != null){
    		head = head.next;
    		len ++;
    	}
    	
    	if(k > len){
    		return h;
    	}
    	
    	ListNode pre = null;
    	ListNode newHead = null;
    	while(len >= k)
    	{
    		ReverseKNodes(ref h, k, ref pre);
    		
    		if(pre == null){
    			newHead = h;
    			pre = h;
    			for(var i =0 ;i < k-1; i++){
    				pre = pre.next;	
    			}
    		}else{
    			for(var i = 0;i < k;i++){
    				pre = pre.next;
    			}
    		}
    		
    		for(var i = 0;i < k;i++){
    			h = h.next;
    		}
    		
    		len -= k;
    	}
    	
    	return newHead;
    }


private void ReverseKNodes(ref ListNode n, int k, ref ListNode preNode)
{
	var stack = new Stack<int>();
	for(var i = 0;i < k; i++){
		stack.Push(n.val);
		n = n.next;
	}
	ListNode end = n;
	
	ListNode tmp = new ListNode(stack.Pop());
	var tmpHead = tmp;
	while(stack.Count > 0){
		var n1 = new ListNode(stack.Pop());
		tmp.next = n1;
		tmp = tmp.next;
	}
	
	tmp.next = end;
	
	if(preNode != null){
		n = tmpHead;
		preNode.next = tmpHead;
	}else{
		n = tmpHead;
	}
}
}

LeetCode -- Reverse Nodes in k-Group

原文：http://blog.csdn.net/lan_liang/article/details/49511523