#1530 - Number of Good Leaf Nodes Pairs

Medium • View on LeetCode • View on GitHub

Problem Description

You are given the root of a binary tree and an integer distance. A pair of two different leaf nodes of a binary tree is said to be good if the length of the shortest path between them is less than or equal to distance.

Return the number of good leaf node pairs in the tree.

Solution

/**
 * 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
 * @param {number} distance
 * @return {number}
 */
var countPairs = function(root, distance) {
  let result = 0;
  traverseTree(root);
  return result;

  function traverseTree(node) {
    if (!node) return [];
    if (!node.left && !node.right) return [1];

    const leftDistances = traverseTree(node.left);
    const rightDistances = traverseTree(node.right);

    for (const left of leftDistances) {
      for (const right of rightDistances) {
        if (left + right <= distance) result++;
      }
    }

    const allDistances = [];
    for (const dist of leftDistances.concat(rightDistances)) {
      if (dist + 1 <= distance) allDistances.push(dist + 1);
    }

    return allDistances;
  }
};