Feat: 124. Binary Tree Maximum Path Sum

Author: HC-kang

binary-tree-maximum-path-sum/HC-kang.ts

@@ -0,0 +1,65 @@
+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;
+  }
+}
+
+/**
+ * https://leetcode.com/problems/binary-tree-maximum-path-sum
+ * T.C. O(n)
+ * S.C. O(n)
+ */
+function maxPathSum(root: TreeNode | null): number {
+  let max = -Infinity;
+
+  function dfs(node: TreeNode | null): number {
+    if (!node) return 0;
+
+    const left = Math.max(0, dfs(node.left));
+    const right = Math.max(0, dfs(node.right));
+
+    max = Math.max(max, node.val + left + right);
+
+    return node.val + Math.max(left, right);
+  }
+
+  dfs(root);
+
+  return max;
+}
+
+/**
+ * iterative using stack
+ * T.C. O(n)
+ * S.C. O(n)
+ */
+function maxPathSum(root: TreeNode | null): number {
+  let max = -Infinity;
+  const stack: Array<TreeNode | null> = [root];
+  const memo = new Map<TreeNode, number>();
+
+  while (stack.length) {
+    const node = stack.pop();
+
+    if (!node) continue;
+
+    if (memo.has(node)) {
+      const left = Math.max(0, node.left ? memo.get(node.left)! : 0);
+      const right = Math.max(0, node.right ? memo.get(node.right)! : 0);
+
+      max = Math.max(max, node.val + left + right);
+
+      memo.set(node, node.val + Math.max(left, right));
+    } else {
+      stack.push(node, node.right, node.left);
+      memo.set(node, 0);
+    }
+  }
+
+  return max;
+}