feat(soobing): week11 > reorder-list

Author: soobing

reorder-list/soobing.ts

@@ -0,0 +1,60 @@
+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 reverseList(head: ListNode | null) {
+  let prev: ListNode | null = null;
+  let cur: ListNode | null = head;
+
+  while (cur) {
+    const next = cur.next;
+    cur.next = prev;
+    prev = cur;
+    cur = next;
+  }
+
+  return prev;
+}
+
+function reorderList(head: ListNode | null): void {
+  if (!head || !head.next) return;
+
+  // 1. 중간 지점 찾기
+  let slow: ListNode | null = head;
+  let fast: ListNode | null = head;
+
+  while (fast && fast.next) {
+    slow = slow!.next;
+    fast = fast.next.next;
+  }
+
+  // 2. 리스트 절단
+  const secondHead = slow!.next;
+  slow!.next = null;
+
+  // 3. 뒤쪽 리스트 뒤집기
+  let second: ListNode | null = reverseList(secondHead);
+
+  // 4. 병합
+  let first: ListNode | null = head;
+
+  while (second) {
+    let tmp1 = first!.next;
+    let tmp2 = second.next;
+
+    first!.next = second;
+    second.next = tmp1;
+
+    first = tmp1;
+    second = tmp2;
+  }
+}