Add week 12 solutions: remove-nth-node-from-end-of-list

Author: gitsunmin

remove-nth-node-from-end-of-list/gitsunmin.ts

@@ -0,0 +1,33 @@
+/**
+ * https://leetcode.com/problems/remove-nth-node-from-end-of-list/
+ * time complexity : O(n)
+ * space complexity : O(1)
+ */
+
+class ListNode {
+    val: number
+    next: ListNode | null
+    constructor(val?: number, next?: ListNode | null) {
+        this.val = (val === undefined ? 0 : val)
+        this.next = (next === undefined ? null : next)
+    }
+}
+
+function removeNthFromEnd(head: ListNode | null, n: number): ListNode | null {
+    const dummy = new ListNode(0, head);
+    let first: ListNode | null = dummy;
+    let second: ListNode | null = dummy;
+
+    for (let i = 0; i <= n; i++) {
+        if (first !== null) first = first.next;
+    }
+
+    while (first !== null) {
+        first = first.next;
+        second = second!.next;
+    }
+
+    if (second !== null && second.next !== null) second.next = second.next.next;
+
+    return dummy.next;
+};