删除单链表倒数第n个节点

基本问题

常规解法

代码实现

/**
*
* Description: 删除单链表倒数第n个节点，常规解法.
*
*  @param  head
*  @param  n
*  @return  ListNode
*/
public   static  ListNode removeNthFromEnd(ListNode head,  int  n) {
if  (head ==  null )
return   null ;
//get length of list
ListNode p = head;
int  len = 0;
while  (p !=  null ) {
len++;
p = p. next ;
}
//if remove first node
int  fromStart = len - n + 1;
if  (fromStart == 1)
return  head. next ;
//remove non-first node
p = head;
int  i = 0;
while  (p !=  null ) {
i++;
if  (i == fromStart - 1) {
p. next  = p. next . next ;
}
p = p. next ;
}
return  head;
}

一次遍历法

代码实现

/**
*
* Description: 删除单链表倒数第n个节点，快慢指针法.
*
*  @param  head
*  @param  n
*  @return  ListNode
*/
public   static  ListNode removeNthFromEnd(ListNode head,  int  n) {
if  (head ==  null )
return   null ;
ListNode fast = head;
ListNode slow = head;
for  ( int  i = 0; i < n; i++) {
fast = fast. next ;
}
//if remove the first node
if  (fast ==  null ) {
head = head. next ;
return  head;
}
while  (fast. next  !=  null ) {
fast = fast. next ;
slow = slow. next ;
}
slow. next  = slow. next . next ;
return  head;
}