add Binary Tree Maximum Path Sum solution

Author: HoonDongKang

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

@@ -0,0 +1,38 @@
+/**
+ * [Problem]: [124 Binary Tree Maximum Path Sum
+ * (https://leetcode.com/problems/binary-tree-maximum-path-sum/description/)
+ */
+/**
+ * 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)
+ *     }
+ * }
+ */
+
+//시간복잡도 O(n)
+//공간복잡도 O(h)
+function maxPathSum(root: TreeNode | null): number {
+    if (!root) return 0;
+    let result = root.val;
+
+    function dfs(node: TreeNode | null) {
+        if (!node) return 0;
+
+        let leftMax = Math.max(dfs(node.left), 0);
+        let rightMax = Math.max(dfs(node.right), 0);
+
+        result = Math.max(node.val + leftMax + rightMax, result);
+
+        return node.val + Math.max(leftMax, rightMax);
+    }
+
+    dfs(root);
+    return result;
+}