added solution for Two Sum BSTs.

problems/two-sum-bsts/README.md

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+# Two Sum BSTs
+
+LeetCode #: [1214](https://leetcode.com/problems/two-sum-bsts/)
+
+Difficulty: Medium.
+
+Topics: Binary search tree.

problems/two-sum-bsts/solution.js

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+const twoSumBSTs = (root1, root2, target) => {
+  if (root1 === null || root2 === null) {
+    return false
+  }
+
+  const sum = root1.val + root2.val
+
+  if (sum === target) {
+    return true
+  } else if (sum < target) {
+    return (
+      twoSumBSTs(root1, root2.right, target) ||
+      twoSumBSTs(root1.right, root2, target)
+    )
+  } else {
+    return (
+      twoSumBSTs(root1, root2.left, target) ||
+      twoSumBSTs(root1.left, root2, target)
+    )
+  }
+}
+
+module.exports = twoSumBSTs

problems/two-sum-bsts/solution.test.js

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+const leettree = require('leettree')
+const twoSumBSTs = require('./solution')
+
+test('Example 1', () => {
+  const root1 = [2, 1, 4]
+  const root2 = [1, 0, 3]
+  const target = 5
+
+  const result = twoSumBSTs(
+    leettree.deserialize(root1),
+    leettree.deserialize(root2),
+    target
+  )
+
+  expect(result).toBe(true)
+})
+
+test('Example 2', () => {
+  const root1 = [0, -10, 10]
+  const root2 = [5, 1, 7, 0, 2]
+  const target = 18
+
+  const result = twoSumBSTs(
+    leettree.deserialize(root1),
+    leettree.deserialize(root2),
+    target
+  )
+
+  expect(result).toBe(false)
+})
+
+test('very small value', () => {
+  const root1 = [2, 1, 4]
+  const root2 = [1, 0, 3]
+  const target = -100
+
+  const result = twoSumBSTs(
+    leettree.deserialize(root1),
+    leettree.deserialize(root2),
+    target
+  )
+
+  expect(result).toBe(false)
+})