choices choices choices

choose.js

function choices(n) {
  var map = {}

  var rand = function (n) {
    return Math.floor(n * Math.random())
  }

  var stride = (n / 2)
  var i = rand(n)
  var max = 0
  
  this.choose = function() {
    if (max === n) {
      return -1
    } else {
      var x = i
      while (map[x]) {
        i = (i + rand(stride)) % n
        x = i
      }
      map[x] = true
      max++
      return x
    }
  }

  return this
}

var c = choices(10)

console.log(c.choose())
console.log(c.choose())
console.log(c.choose())
console.log(c.choose())
console.log(c.choose())
console.log(c.choose())
console.log(c.choose())
console.log(c.choose())
console.log(c.choose())
console.log(c.choose())
console.log(c.choose())
console.log(c.choose())

/**
> node choose
2
6
8
4
5
9
0
3
7
1
-1
-1
*/