#1443 - Minimum Time to Collect All Apples in a Tree

Problem Description

Given an undirected tree consisting of n vertices numbered from 0 to n-1, which has some apples in their vertices. You spend 1 second to walk over one edge of the tree. Return the minimum time in seconds you have to spend to collect all apples in the tree, starting at vertex 0 and coming back to this vertex.

The edges of the undirected tree are given in the array edges, where edges[i] = [ai, bi] means that exists an edge connecting the vertices ai and bi. Additionally, there is a boolean array hasApple, where hasApple[i] = true means that vertex i has an apple; otherwise, it does not have any apple.

Solution

/**
 * @param {number} n
 * @param {number[][]} edges
 * @param {boolean[]} hasApple
 * @return {number}
 */
var minTime = function(n, edges, hasApple) {
  const map = new Map();
  const seen = new Set();
  let time = 0;

  edges.forEach(([value, key]) => map.set(key, value));
  for (let i = n - 1; i >= 0; i--) {
    if (hasApple[i]) {
      dfs(i);
    }
  }

  function dfs(key) {
    if (key === 0 || seen.has(key)) return;
    seen.add(key);
    time += 2;
    dfs(map.get(key));
  }

  return time;
};