Add solution #124

Author: JoshCrozier

README.md

@@ -127,6 +127,7 @@
 119|[Pascal's Triangle II](./0119-pascals-triangle-ii.js)|Easy|
 120|[Triangle](./0120-triangle.js)|Medium|
 121|[Best Time to Buy and Sell Stock](./0121-best-time-to-buy-and-sell-stock.js)|Easy|
+124|[Binary Tree Maximum Path Sum](./0124-binary-tree-maximum-path-sum.js)|Hard|
 125|[Valid Palindrome](./0125-valid-palindrome.js)|Easy|
 128|[Longest Consecutive Sequence](./0128-longest-consecutive-sequence.js)|Medium|
 131|[Palindrome Partitioning](./0131-palindrome-partitioning.js)|Medium|

solutions/0124-binary-tree-maximum-path-sum.js

@@ -0,0 +1,41 @@
+/**
+ * 124. Binary Tree Maximum Path Sum
+ * https://leetcode.com/problems/binary-tree-maximum-path-sum/
+ * Difficulty: Hard
+ *
+ * A path in a binary tree is a sequence of nodes where each pair of adjacent nodes in the
+ * sequence has an edge connecting them. A node can only appear in the sequence at most
+ * once. Note that the path does not need to pass through the root.
+ *
+ * The path sum of a path is the sum of the node's values in the path.
+ *
+ * Given the root of a binary tree, return the maximum path sum of any non-empty path.
+ */
+
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val, left, right) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.left = (left===undefined ? null : left)
+ *     this.right = (right===undefined ? null : right)
+ * }
+ */
+/**
+ * @param {TreeNode} root
+ * @return {number}
+ */
+var maxPathSum = function(root) {
+  let result = -Infinity;
+
+  function traverse(node) {
+    if (!node) return 0;
+    const leftValue = Math.max(traverse(node.left), 0);
+    const rightValue = Math.max(traverse(node.right), 0);
+    result = Math.max(result, node.val + leftValue + rightValue);
+    return node.val + Math.max(leftValue, rightValue);
+  }
+
+  traverse(root);
+
+  return result;
+};