[1lsang] WEEK 04 solutions

maximum-depth-of-binary-tree/1lsang.ts

@@ -0,0 +1,35 @@
+/**
+ * Definition for a binary tree node.
+ * class TreeNode {
+ *     val: number
+ *     left: TreeNode | null
+ *     right: TreeNode | null
+ *     constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
+ *         this.val = (val===undefined ? 0 : val)
+ *         this.left = (left===undefined ? null : left)
+ *         this.right = (right===undefined ? null : right)
+ *     }
+ * }
+ */
+
+function maxDepth(root: TreeNode | null): number {
+  // DFS (혹은 BFS) 후 깊이 체크하기
+  if (!root) return 0;
+
+  const stack: [TreeNode, number][] = [[root, 1]];
+  let maxDepth = 0;
+
+  while (stack.length > 0) {
+    const [node, depth] = stack.pop()!;
+    maxDepth = Math.max(maxDepth, depth);
+
+    if (node.right) {
+      stack.push([node.right, depth + 1]);
+    }
+    if (node.left) {
+      stack.push([node.left, depth + 1]);
+    }
+  }
+
+  return maxDepth;
+};

merge-two-sorted-lists/1lsang.ts

@@ -0,0 +1,54 @@
+/**
+ * Definition for singly-linked 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)
+ *     }
+ * }
+ */
+
+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 mergeTwoLists(list1: ListNode | null, list2: ListNode | null): ListNode | null {
+  // list1과 list2의 val을 비교해나가면서 새로운 list 생성
+  // 1. list1 없으면 list2 return
+  if (!list1) return list2;
+  // 2. list2 없으면 list1 return 
+  if (!list2) return list1;
+
+  const list = new ListNode(-101);
+
+  let listNode = list;
+  let listNode1: ListNode | null = list1;
+  let listNode2: ListNode | null = list2;
+
+  while (listNode1 && listNode2) {
+    if (listNode1.val > listNode2.val) {
+      listNode.next = new ListNode(listNode2.val, null);
+      listNode2 = listNode2.next;
+    }
+    else {
+      listNode.next = new ListNode(listNode1.val, null);
+      listNode1 = listNode1.next;
+    }
+    listNode = listNode.next;
+  }
+  if (!listNode1) {
+    listNode.next = listNode2;
+  }
+  else if (!listNode2) {
+    listNode.next = listNode1;
+  }
+
+  return list.next;
+};