24.8.22 LeetCode Hot100 linkedList

src/main/java/com/cool/hot100/linkedlist/Num19.java

@@ -0,0 +1,63 @@
+package com.cool.hot100.linkedlist;
+
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class Num19 {
+
+
+    /**
+     * Date 2024/8/22
+     * DayNumber 2
+     * Hard 2
+     */
+    public ListNode removeNthFromEnd(ListNode head, int n) {
+        // Ans1 Space O(n)
+//        List<ListNode> list=new ArrayList<>();
+//        ListNode node=head;
+//        while (node!=null){
+//            list.add(node);
+//            node=node.next;
+//        }
+//        int index=list.size()-n;
+//        if(index==0){
+//            return list.size()>1?list.get(1):null;
+//        }
+//        if(index==list.size()){
+//            list.get(list.size()-1).next=null;
+//            return list.get(0);
+//        }
+//        ListNode temp=null;
+//        if(index+1<list.size()){
+//            temp=list.get(index+1);
+//        }
+//        list.get(index-1).next=temp;
+//        return list.get(0);
+        // Ans2
+        if(head==null) return null;
+        ListNode fast=head;
+        ListNode slow=null;
+        while (n>0){
+            fast=fast.next;
+            n--;
+        }
+        while (fast!=null){
+            fast=fast.next;
+            slow=slow==null?head:slow.next;
+        }
+        if (slow == null) {
+            return head.next;
+        }
+        slow.next=slow.next.next;
+        return head;
+    }
+
+    @Test
+    public void test() {
+        ListNode node = new ListNode(1);
+        ListNode node1 = new ListNode(2, node);
+        removeNthFromEnd(node1, 1);
+    }
+}