add Reorder List solution

Author: HoonDongKang

reorder-list/HoonDongKang.ts

@@ -0,0 +1,84 @@
+/**
+ * [Problem]: [143] Reorder List
+ * (https://leetcode.com/problems/reorder-list/)
+ */
+
+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;
+    }
+}
+
+/**
+ Do not return anything, modify head in-place instead.
+ */
+function reorderList(head: ListNode | null): void {
+    //시간복잡도 O(n)
+    //공간복잡도 O(n)
+    function stackFunc(head: ListNode | null): void {
+        if (!head || !head.next) return;
+
+        const stack: ListNode[] = [];
+        let node: ListNode | null = head;
+
+        while (node) {
+            stack.push(node);
+            node = node.next;
+        }
+
+        const length = stack.length;
+        node = head;
+
+        for (let i = 0; i < Math.floor(length / 2); i++) {
+            const tail = stack.pop()!;
+            const next: ListNode | null = node.next;
+
+            node.next = tail;
+            tail.next = next;
+
+            node = next!;
+        }
+
+        node.next = null;
+    }
+    //시간복잡도 O(n)
+    //공간복잡도 O(1)
+    function twoPointerFunc(head: ListNode | null): void {
+        if (!head || !head.next) return;
+
+        let slow = head;
+        let fast = head;
+        while (fast && fast.next && fast.next.next) {
+            slow = slow.next!;
+            fast = fast.next.next;
+        }
+
+        let prev: ListNode | null = null;
+        let curr = slow.next;
+        slow.next = null;
+
+        while (curr) {
+            const next = curr.next;
+            curr.next = prev;
+            prev = curr;
+            curr = next;
+        }
+
+        let first = head;
+        let second = prev;
+
+        while (second) {
+            const tmp1 = first!.next;
+            const tmp2 = second.next;
+
+            first!.next = second;
+            second.next = tmp1;
+
+            first = tmp1!;
+            second = tmp2;
+        }
+    }
+}