add max path sum in binary tree question

Author: betomoedano

binary-trees/max-path-sum-in-binary-tree.js

@@ -0,0 +1,29 @@
+// Time O(n)
+// Space O(log n) because we are dealing with a binary tree and at most
+// we will have log n calls on the call stack
+function maxPathSum(tree) {
+  const [_, maxSum] = findMaxSum(tree);
+  return maxSum;
+}
+
+function findMaxSum(tree) {
+  if (tree === null) return [0, -Infinity];
+
+  const [leftMaxSumAsBranch, leftMaxPathSum] = findMaxSum(tree.left);
+  const [rightMaxSumAsBranch, rightMaxPathSum] = findMaxSum(tree.right);
+  const maxChildSumAsBranch = Math.max(leftMaxSumAsBranch, rightMaxSumAsBranch);
+
+  const { value } = tree;
+  const maxSumAsBranch = Math.max(maxChildSumAsBranch + value, value);
+  const maxSumAsRootNode = Math.max(
+    leftMaxSumAsBranch + value + rightMaxSumAsBranch,
+    maxSumAsBranch
+  );
+  const maxPathSum = Math.max(
+    leftMaxPathSum,
+    rightMaxPathSum,
+    maxSumAsRootNode
+  );
+
+  return [maxSumAsBranch, maxPathSum];
+}