답안

const graph = {1: [2, 3, 4],
				 2: [1, 3, 4, 5, 6],
				 3: [1, 2, 7],
				 4: [1, 2, 5, 6],
				 5: [2, 4, 6, 7],
				 6: [2, 4, 5, 7],
				 7: [3, 5, 6]};

const user_input = prompt('입력해주세요').split(' ');
const start = parseInt(user_input[0], 10);
const end = parseInt(user_input[1], 10);

let queue = [start];
let visited = [];

function sol(n, visited){
  let node = n[n.length-1];
  let length = 0;

  if (node == end) {
    return visited.length;
  }

	if (visited.includes(node)) {
    return visited.length;
  } else {
    visited.push(node);
  }
  let max = [];

	for (let next_node in graph[node]) {
    n.push(graph[node][next_node]);

    max.push(length, sol(n, visited));
    length = Math.max.apply(null, max);

		queue.pop();
  }
	return length;
}

console.log(sol(queue, visited));