permCheck-7.js

function solution(A) {
  // write your code in JavaScript (Node.js 8.9.4)

  A.sort((a, b) => a - b);
  if (A[0] != 1) {
    return 0;
  }
  for (let i = 0; i < A.length - 1; i++) {
    if (A[i + 1] != A[i] + 1) {
      return 0;
    }
  }
  return 1;
}