Add RemoveNthNodeFromLinkedListEnd task solution

Author: andrei-punko

src/main/java/by/andd3dfx/collections/RemoveNthNodeFromLinkedListEnd.java

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+package by.andd3dfx.collections;
+
+import lombok.AllArgsConstructor;
+import lombok.NoArgsConstructor;
+
+/**
+ * <pre>
+ * <a href="https://leetcode.com/problems/remove-nth-node-from-end-of-list/">Task description</a>
+ *
+ * Given the head of a linked list, remove the nth node from the end of the list and return its head.
+ *
+ * Example 1:
+ * Input: head = [1,2,3,4,5], n = 2
+ * Output: [1,2,3,5]
+ *
+ * Example 2:
+ * Input: head = [1], n = 1
+ * Output: []
+ *
+ * Example 3:
+ * Input: head = [1,2], n = 1
+ * Output: [1]
+ *
+ * Constraints:
+ *     The number of nodes in the list is sz.
+ *     1 <= sz <= 30
+ *     0 <= Node.val <= 100
+ *     1 <= n <= sz
+ * </pre>
+ *
+ * @see <a href="https://youtu.be/Ant-eAAwyx8">Video solution</a>
+ */
+public class RemoveNthNodeFromLinkedListEnd {
+
+    @NoArgsConstructor
+    @AllArgsConstructor
+    public static class ListNode {
+
+        int val;
+        ListNode next;
+
+        ListNode(int val) {
+            this.val = val;
+        }
+    }
+
+    public static ListNode removeNthFromEnd(ListNode head, int n) {
+        var newHead = new ListNode();
+        newHead.next = head;
+
+        var first = newHead;
+        var second = newHead;
+
+        for (var i = 0; i < n; i++) {
+            second = second.next;
+        }
+
+        while (second.next != null) {
+            first = first.next;
+            second = second.next;
+        }
+
+        first.next = first.next.next;
+
+        return newHead.next;
+    }
+}

src/test/java/by/andd3dfx/collections/RemoveNthNodeFromLinkedListEndTest.java

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+package by.andd3dfx.collections;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import by.andd3dfx.collections.RemoveNthNodeFromLinkedListEnd.ListNode;
+import org.junit.Test;
+
+public class RemoveNthNodeFromLinkedListEndTest {
+
+    @Test
+    public void removeNthFromEnd1() {
+        var head = new ListNode(1,
+            new ListNode(2, new ListNode(3, new ListNode(4, new ListNode(5)))));
+
+        var result = RemoveNthNodeFromLinkedListEnd.removeNthFromEnd(head, 2);
+
+        assertThat(result.val).isEqualTo(1);
+        assertThat(result.next.val).isEqualTo(2);
+        assertThat(result.next.next.val).isEqualTo(3);
+        assertThat(result.next.next.next.val).isEqualTo(5);
+        assertThat(result.next.next.next.next).isNull();
+    }
+
+    @Test
+    public void removeNthFromEnd2() {
+        var head = new ListNode(1);
+
+        var result = RemoveNthNodeFromLinkedListEnd.removeNthFromEnd(head, 1);
+
+        assertThat(result).isNull();
+    }
+
+    @Test
+    public void removeNthFromEnd3() {
+        var head = new ListNode(1, new ListNode(2));
+
+        var result = RemoveNthNodeFromLinkedListEnd.removeNthFromEnd(head, 1);
+
+        assertThat(result.val).isEqualTo(1);
+        assertThat(result.next).isNull();
+    }
+}