// https://www.freecodecamp.org/learn/coding-interview-prep/data-structures/depth-first-search

function dfs(graph, root) {
  const n_nodes = graph[0].length;
  const reachable = new Set([root]);
  const stack = [root];
  while (stack.length) {
    const node = stack.pop();
    for (let i = 0; i < n_nodes; i++) {
      if (graph[node][i] > 0 && !reachable.has(i)) {
        reachable.add(i);
        stack.push(i);
      }
    }
  }
  return Array.from(reachable);
}

var exDFSGraph = [
  [0, 1, 0, 0],
  [1, 0, 1, 0],
  [0, 1, 0, 1],
  [0, 0, 1, 0],
];
console.log(dfs(exDFSGraph, 3));