busroutes.js

const ExamRoom = function (n) {
  let a = [];
  return { seat, leave };
  function seat() {
    if (a.length == 0) {
      a.push(0);
      return 0;
    }
    let dis = Math.max(a[0], n - 1 - a[a.length - 1]);
    for (let i = 1; i < a.length; i++)
      dis = Math.max(dis, (a[i] - a[i - 1]) >> 1);
    if (a[0] == dis) {
      a.unshift(0);
      return 0;
    }
    for (let i = 1; i < a.length; i++) {
      if ((a[i] - a[i - 1]) >> 1 == dis) {
        a.splice(i, 0, (a[i] + a[i - 1]) >> 1);
        return a[i];
      }
    }
    a.push(n - 1);
    return n - 1;
  }
  function leave(p) {
    for (let i = 0; i < a.length; i++) {
      if (a[i] == p) {
        a.splice(i, 1);
        break;
      }
    }
  }
};

let examRoom = new ExamRoom(10);
console.log(examRoom.seat()); // return 0, no one is in the room, then the student sits at seat number 0.
console.log(examRoom.seat()); // return 9, the student sits at the last seat number 9.
console.log(examRoom.seat()); // return 4, the student sits at the last seat number 4.
console.log(examRoom.seat()); // return 2, the student sits at the last seat number 2.
console.log(examRoom.leave(4));
console.log(examRoom.seat()); // return 5, the student sits at the last seat number 5.