[reeseo3o] WEEK 04 Solutions

maximum-subarray/reeseo3o.js

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+/** 
+ * DFS
+ * Time complexity: O(n)
+ * Space complexity: O(h) - h is the height of the tree, worst case O(n)
+ */
+const maxDepth = (root) => {
+  if (root === null) return 0;
+
+  const leftDepth = maxDepth(root.left);
+  const rightDepth = maxDepth(root.right);
+
+  return 1 + Math.max(leftDepth, rightDepth);
+};
+
+/**
+ * BFS
+ * Time complexity: O(n)
+ * Space complexity: O(n)
+ */
+const maxDepthBFS = (root) => {
+  if (root === null) return 0;
+
+  const queue = [root];
+  let depth = 0;
+
+  while (queue.length > 0) {
+    const levelSize = queue.length;
+
+    for (let i = 0; i < levelSize; i++) {
+      const node = queue.shift();
+      if (node.left) queue.push(node.left);
+      if (node.right) queue.push(node.right);
+    }
+
+    depth++;
+  }
+
+  return depth;
+};

merge-two-sorted-lists/reeseo3o.js

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+/**
+ * 1. Recursive approach
+ * Time complexity: O(n + m)
+ * Space complexity: O(n + m)
+ */
+// const mergeTwoLists = (list1, list2) => {
+//     if (!list1) return list2;
+//     if (!list2) return list1;
+//
+//     if (list1.val <= list2.val) {
+//         list1.next = mergeTwoLists(list1.next, list2);
+//         return list1;
+//     } else {
+//         list2.next = mergeTwoLists(list1, list2.next);
+//         return list2;
+//     }
+// };
+
+/**
+ * 2. Iterative approach + Dummy Node
+ * Time complexity: O(n + m)
+ * Space complexity: O(1)
+ */
+const mergeTwoLists = (list1, list2) => {
+    const dummy = new ListNode(-1);
+    let current = dummy;
+
+    while (list1 !== null && list2 !== null) {
+        if (list1.val <= list2.val) {
+            current.next = list1;
+            list1 = list1.next;
+        } else {
+            current.next = list2;
+            list2 = list2.next;
+        }
+        current = current.next;
+    }
+
+    current.next = list1 ?? list2;
+
+    return dummy.next;
+};