AlgoDaily - Counting Univalued Subtrees

Good morning! Here's our prompt for today.

Question

Can you count all the univalued subtrees in a binary tree, as shown in the figure below?

The Problem

We are given a binary tree. The challenge is to count all the univalued subtrees in the tree. Just to recall, a subtree is any node along with its descendants. The root and all its descendants form the entire tree. A univalued subtree is therefore a subtree in which all the nodes have the same keys. The figure below shows all the univalued subtrees of the binary tree of the previous figure.

Try to solve this here or in Interactive Mode.

How do I practice this challenge?

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var assert = require('assert');
​
function countUniValueSubtrees(root) {
  let count = 0;
  if (!root) {
    return 0;
  }
  isUniValHelper(root, count);
  return count;
}
​
function isUniValHelper(node, count) {
  // Base case: if both children are null, we know the node is a univalue, we can increment count and return true
  if (node.left === null && node.right === null) {
    count++;
    return true;
  }
​
  // Check isUniVal for each child search tree
  let isUniVal = true;
  if (node.left !== null) {
    isUniVal =
      isUniValHelper(node.left) && isUniVal && node.left.val === node.val;
  }
  if (node.right !== null) {
    isUniVal =
      isUniValHelper(node.right) && isUniVal && node.right.val === node.val;
  }
​

Here's how we would solve this problem...

How do I use this guide?

Question

The Problem

Try to solve this here or in Interactive Mode.

Here's how we would solve this problem...

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