LeetCode - Medium - 19

3. 移除a所指向节点。

4. 返回链头。

方法二：别人写的，思路与方法一的相同。

Submission

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import com.lun.util.SinglyLinkedList.ListNode;

public class RemoveNthNodeFromEndOfList {

// 方法一：我写的

public ListNode removeNthFromEnd1(ListNode head, int n) {

if (head == null || n <= 0)

return head;

int count = 1;

ListNode fakeHead = new ListNode(-1, head);

ListNode p1 = head, p2 = head.next, prev = fakeHead;

while (p2 != null && count < n) {

p2 = p2.next;

count++;

}

if (n != count)

return fakeHead.next;// count > 链表长度的情况

// 齐步走

while (p2 != null) {

prev = p1;

p1 = p1.next;

p2 = p2.next;

}

// 移除

prev.next = p1.next;

p1.next = null; // help GC

p2 = fakeHead.next;

fakeHead.next = null; // help GC

return p2;

}

// 方法二：别人写的

public ListNode removeNthFromEnd2(ListNode head, int n) {

ListNode start = new ListNode(0);

ListNode slow = start, fast = start;

slow.next = head;

// Move fast in front so that the gap between slow and fast becomes n

for (int i = 1; i <= n + 1; i++) {

fast = fast.next;

}

// Move fast to the end, maintaining the gap

while (fast != null) {

slow = slow.next;

fast = fast.next;

}

// Skip the desired node

slow.next = slow.next.next;

return start.next;

}

}

Test

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import static org.junit.Assert.*;

import org.junit.Test;

import com.lun.util.SinglyLinkedList;

import com.lun.util.SinglyLinkedList.ListNode;

public class RemoveNthNodeFromEndOfListTest {

@Test

public void test1() {

RemoveNthNodeFromEndOfList obj = new RemoveNthNodeFromEndOfList();

ListNode original1 = SinglyLinkedList.ints2List(1, 2, 3, 4, 5);

ListNode expected1 = SinglyLinkedList.ints2List(1, 2, 3, 5);

assertTrue(SinglyLinkedList.areTwoListEqual(expected1, obj.removeNthFromEnd1(original1, 2)));

ListNode original2 = new ListNode(1);

assertNull(obj.removeNthFromEnd1(original2, 1));

ListNode original3 = SinglyLinkedList.ints2List(1, 2);

ListNode expected3 = new ListNode(1);

assertTrue(SinglyLinkedList.areTwoListEqual(expected3, obj.removeNthFromEnd1(original3, 1)));

}

@Test

public void test2() {

RemoveNthNodeFromEndOfList obj = new RemoveNthNodeFromEndOfList();

ListNode original1 = SinglyLinkedList.ints2List(1, 2, 3, 4, 5);

ListNode expected1 = SinglyLinkedList.ints2List(1, 2, 3, 5);

最后

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