36 - 翻转链表 II

2017.9.18

/**
 * Definition for ListNode
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */


public class Solution {
    /*
     * @param head: ListNode head is the head of the linked list 
     * @param m: An integer
     * @param n: An integer
     * @return: The head of the reversed ListNode
     */
    	public ListNode reverseBetween(ListNode head, int m, int n) {
        // write your code here
        if( m >= n){
			return head;
		}
		ListNode pre = new ListNode(-1);
		// 指向第m个结点之前的那个结点
		pre.next = head;
		// 指向第m个结点
		ListNode theM = head;
		int tmpM = m;
		while(pre != null && theM != null && m > 1){
			pre = pre.next;
			theM = theM.next;
			m--;
		}
		if(m > 1){
			return null;
		}
		while(theM.next != null && n > tmpM){
			ListNode tmp = theM.next;
			theM.next = tmp.next;
			tmp.next = pre.next;
			pre.next = tmp;
			n --;
		}
		if(n > tmpM){
			return null;
		}
		if(tmpM == 0 || tmpM == 1){
		    return pre.next;
		}
		return head;
    }
}