From efb982a11b2ac6e92fbcf584728f2be077b5313d Mon Sep 17 00:00:00 2001
From: whai <lkwhai@163.com>
Date: Sun, 31 Dec 2023 21:01:41 +0800
Subject: [PATCH] =?UTF-8?q?=E4=BF=AE=E6=94=B9=E5=88=86=E7=B1=BB?=
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---
 .../leetCode/LinkedList/LeetCode19.java       | 144 ++++++++++++++++++
 1 file changed, 144 insertions(+)
 create mode 100644 src/main/java/cn/whaifree/leetCode/LinkedList/LeetCode19.java

diff --git a/src/main/java/cn/whaifree/leetCode/LinkedList/LeetCode19.java b/src/main/java/cn/whaifree/leetCode/LinkedList/LeetCode19.java
new file mode 100644
index 0000000..75a1f8f
--- /dev/null
+++ b/src/main/java/cn/whaifree/leetCode/LinkedList/LeetCode19.java
@@ -0,0 +1,144 @@
+package cn.whaifree.leetCode.LinkedList;
+
+import cn.whaifree.leetCode.model.ListNode;
+import org.junit.Test;
+
+import java.util.Deque;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Stack;
+
+public class LeetCode19 {
+
+    @Test
+    public void test() {
+        Solution2 solution = new Solution2();
+        ListNode listNode = solution.removeNthFromEnd(ListNode.listNodeFromArray(new int[]{1,2,3,4}), 3);
+        ListNode.printList(listNode);
+
+    }
+
+    /**
+     * Definition for singly-linked list.
+     * public class ListNode {
+     *     int val;
+     *     ListNode next;
+     *     ListNode() {}
+     *     ListNode(int val) { this.val = val; }
+     *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
+     * }
+     */
+    class Solution {
+
+
+        /**
+         * 链表中结点的数目为 sz
+         * 1 <= sz <= 30
+         * 0 <= Node.val <= 100
+         * 1 <= n <= sz
+         *
+         * 时间复杂度：O(Length)
+         * 空间复杂度：O(1)
+         *
+         * @param head
+         * @param n
+         * @return
+         */
+        public ListNode removeNthFromEnd(ListNode head, int n) {
+
+            // 空链表
+            if (head == null) {
+                return head;
+            }
+            int length = getLength(head);
+            // 删除头
+            if (n == length) {
+                head = head.next;
+                return head;
+            }
+
+            int find = length - n;
+            ListNode index = head;
+            for (int i = 0; i < find - 1; i++) {
+                index = index.next;
+            }
+            index.next = index.next.next;
+            return head;
+        }
+
+        int getLength(ListNode head) {
+            int length = 0;
+            ListNode index = head;
+            while (index != null) {
+                index = index.next;
+                length++;
+            }
+            return length;
+        }
+    }
+
+
+    class Solution1 {
+
+
+        /**
+         * 栈
+         * 时间复杂度：O(Length)
+         * 空间复杂度：O(Length)
+         *
+         * 修改多使用这个栈会更快
+         * LinkedList比Stack快的原因如下1：
+         *     基于数组实现：Stack基于数组实现，随机访问（查找）效率更高，增删改效率较低。
+         *     基于链表实现：LinkedList基于链表实现，增删改效率更高，随机访问（查找）效率较低。
+         * 对于频繁的插入、删除操作，利用LinkedList实现栈自然比Stack快很多。
+         * @param head
+         * @param n
+         * @return
+         */
+        public ListNode removeNthFromEnd(ListNode head, int n) {
+
+            ListNode dummy = new ListNode(0, head);
+            Deque<ListNode> stack = new LinkedList<ListNode>();
+            // 双端队列
+            ListNode index = dummy;
+            while (index != null) {
+                stack.push(index);
+                index = index.next;
+            }
+            for (int i = 0; i < n; i++) {
+                stack.pop();
+            }
+            ListNode peek = stack.peek();
+            peek.next = peek.next.next;
+            return dummy.next;
+        }
+    }
+
+
+    class Solution2 {
+
+
+        /**
+         * 双指针 快慢节点追逐：
+         *          两个节点的差值为n，快指针走完了，慢指针就是了
+         *
+         * @param head
+         * @param n
+         * @return
+         */
+        public ListNode removeNthFromEnd(ListNode head, int n) {
+            ListNode dummy = new ListNode(0, head);
+            ListNode fast = dummy;
+            ListNode slow = dummy;
+            for (int i = 0; i <= n; i++) {
+                fast = fast.next;
+            }
+            while (fast!= null) {
+                fast = fast.next;
+                slow = slow.next;
+            }
+            slow.next = slow.next.next;
+            return dummy.next;
+        }
+    }
+}