binary tree maximum path sum solution

Author: hyer0705

binary-tree-maximum-path-sum/hyer0705.ts

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+/**
+ * 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)
+ *     }
+ * }
+ */
+
+// Time Complexity: O(n)
+// Space Complexity: O(h) where h is the height of the tree
+function maxPathSum(root: TreeNode | null): number {
+  let maximumSum = -Infinity;
+
+  const dfs = (node: TreeNode | null) => {
+    if (!node) return 0;
+
+    let leftResult = dfs(node.left);
+    let rightResult = dfs(node.right);
+
+    leftResult = Math.max(0, leftResult);
+    rightResult = Math.max(0, rightResult);
+
+    maximumSum = Math.max(maximumSum, node.val + leftResult + rightResult);
+
+    return node.val + Math.max(leftResult, rightResult);
+  };
+
+  dfs(root);
+
+  return maximumSum;
+}