Merge pull request #38 from jeantimex/sum-root-to-leaf-numbers

Added sum root to leaf numbers problem.

Author: jeantimex

README.md

@@ -34,6 +34,7 @@ A collection of JavaScript problems and solutions for studying algorithms.
 - [Populating Next Right Pointers in Each Node](src/tree/populating-next-right-pointers-in-each-node.js)
 - [Populating Next Right Pointers in Each Node II](src/tree/populating-next-right-pointers-in-each-node-ii.js)
 - [Binary Tree Maximum Path Sum](src/tree/binary-tree-maximum-path-sum.js)
+- [Sum Root to Leaf Numbers](src/tree/sum-root-to-leaf-numbers.js)
 
 ### Dynamic Programming
 

src/tree/__tests__/sum-root-to-leaf-numbers-test.js

@@ -0,0 +1,16 @@
+import { assert } from 'chai';
+import { serializeTree, deserializeTree } from 'utils/tree-util';
+import sumNumbers from '../sum-root-to-leaf-numbers';
+
+describe('Sum Root to Leaf Numbers', () => {
+  const testCases = [['null', 0], ['1', 1], ['1,2', 12], ['1,2,3', 25]];
+
+  testCases.map((testCase, index) => {
+    it(`should calculate the sum from roof to leaf nodes for tree ${testCase[0]}`, () => {
+      const root = deserializeTree(testCase[0]);
+      const expected = testCase[1];
+      const actual = sumNumbers(root);
+      assert.equal(actual, expected);
+    });
+  });
+});

src/tree/sum-root-to-leaf-numbers.js

@@ -0,0 +1,43 @@
+/**
+ * Given a binary tree containing digits from 0-9 only, each root-to-leaf path could represent a number.
+ * 
+ * An example is the root-to-leaf path 1->2->3 which represents the number 123.
+ * 
+ * Find the total sum of all root-to-leaf numbers.
+ * 
+ * For example,
+ * 
+ *     1
+ *    / \
+ *   2   3
+ * The root-to-leaf path 1->2 represents the number 12.
+ * The root-to-leaf path 1->3 represents the number 13.
+ * 
+ * Return the sum = 12 + 13 = 25.
+ */
+
+/**
+ * @param {TreeNode} root
+ * @return {number}
+ */
+const sumNumbers = root => {
+  return helper(root, 0);
+};
+
+const helper = (node, sum) => {
+  if (!node) {
+    return 0;
+  }
+
+  const { left, right } = node;
+
+  sum = 10 * sum + node.val;
+
+  if (!left && !right) {
+    return sum;
+  }
+
+  return helper(left, sum) + helper(right, sum);
+};
+
+export default sumNumbers;