19. Remove Nth Node From End of List

Author: zhangbo54

src/leetcode/_19_/ListNode.java

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+package leetcode._19_;
+
+/**
+ * Created by zhangbo54 on 2019-03-06.
+ */
+public class ListNode {
+    int val;
+    ListNode next;
+
+    ListNode(int x) {
+        val = x;
+    }
+
+    public int getVal() {
+        return val;
+    }
+
+    public void setVal(int val) {
+        this.val = val;
+    }
+
+    public ListNode getNext() {
+        return next;
+    }
+
+    public ListNode setNext(ListNode next) {
+        this.next = next;
+        return this;
+    }
+
+    @Override
+    public String toString() {
+        StringBuilder sb = new StringBuilder();
+        ListNode head = this;
+        while (head != null) {
+            sb.append(head.val).append("->");
+            head = head.next;
+        }
+        sb.delete(sb.length() - 2, sb.length());
+        return sb.toString();
+    }
+}

src/leetcode/_19_/Main.java

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+package leetcode._19_;
+
+/**
+ * Created by zhangbo54 on 2019-03-04.
+ */
+public class Main {
+    public static void main(String[] args) {
+        ListNode node = new ListNode(1).setNext(new ListNode(2).setNext(new ListNode(3).setNext(new ListNode(4).setNext(new ListNode(5)))));
+        // ListNode node = new ListNode(1).setNext(new ListNode(2));
+        Solution solution = new Solution();
+        ListNode listNode = solution.removeNthFromEnd(node, 2);
+        System.out.println(listNode.toString());
+    }
+}
+

src/leetcode/_19_/Solution.java

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+package leetcode._19_;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ * int val;
+ * ListNode next;
+ * ListNode(int x) { val = x; }
+ * }
+ */
+class Solution {
+    public ListNode removeNthFromEnd(ListNode head, int n) {
+        ListNode node1 = head;
+        ListNode node2 = head;
+        // 由于题目中说到 n 永远有效，所以不做 nodeList 长度不足n的判断
+        for (int i = 0; i < n; i++) {
+            node1 = node1.next;
+        }
+        if (node1 == null) {
+            return head.next;
+        }
+        node1 = node1.next;
+
+        while (node1 != null) {
+            node1 = node1.next;
+            node2 = node2.next;
+        }
+        node2.next = node2.next.next;
+        return head;
+    }
+}

src/leetcode/_19_/solution.md

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+### [19\. Remove Nth Node From End of List](https://leetcode.com/problems/remove-nth-node-from-end-of-list/)
+
+Difficulty: **Medium**
+
+
+Given a linked list, remove the _n_-th node from the end of list and return its head.
+
+**Example:**
+
+```
+Given linked list: 1->2->3->4->5, and n = 2.
+
+After removing the second node from the end, the linked list becomes 1->2->3->5.
+```
+
+**Note:**
+
+Given _n_ will always be valid.
+
+**Follow up:**
+
+Could you do this in one pass?
+
+
+#### Solution
+
+Language: **Java**
+
+```java
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ * int val;
+ * ListNode next;
+ * ListNode(int x) { val = x; }
+ * }
+ */
+class Solution {
+    public ListNode removeNthFromEnd(ListNode head, int n) {
+        ListNode node1 = head;
+        ListNode node2 = head;
+        // 由于题目中说到 n 永远有效，所以不做 nodeList 长度不足n的判断
+        for (int i = 0; i < n; i++) {
+            node1 = node1.next;
+        }
+        if (node1 == null) {
+            return head.next;
+        }
+        node1 = node1.next;
+​
+        while (node1 != null) {
+            node1 = node1.next;
+            node2 = node2.next;
+        }
+        node2.next = node2.next.next;
+        return head;
+    }
+}
+            node2 = node2.next;
+```
+![](https://ws3.sinaimg.cn/large/006tKfTcgy1g0ugblbxe4j310o0u0dk3.jpg)