Generate random integer with ALL digits from 1-9

Question

How do I generate a 9-digit integer that has all digits from 1-9? Like 123456798, 981234765, 342165978, etc.

Doing this:

var min = 100000000;
var max = 999999999;
var num = Math.floor(Math.random() * (max - min + 1)) + min;

does not work give me the integer that I want most of the time (does not have ALL digits from 1 to 9).

111111119 is not acceptable because each number must have at least one "1" in it, "2", "3", ... and a "9" in it.

well for starters change the min to 111111111 – Banana Mar 28 '14 at 08:22 — Banana, Mar 28 '14 at 08:22
That's not really random, is it? – CodingIntrigue Mar 28 '14 at 08:22 — CodingIntrigue, Mar 28 '14 at 08:22

score 11 · Accepted Answer · edited May 23 '17 at 11:43

Just start with the string 123456789 and shuffle it randomly as described in How do I shuffle the characters in a string in JavaScript?

String.prototype.shuffle = function () {
    var a = this.split(""),
        n = a.length;

    for(var i = n - 1; i > 0; i--) {
        var j = Math.floor(Math.random() * (i + 1));
        var tmp = a[i];
        a[i] = a[j];
        a[j] = tmp;
    }
    return a.join("");
}

thefourtheye · Answer 2 · 2014-04-04T05:35:48.120

4

This program, with little tweaks, will be a good addition to your custom utility belt.

Adapted from the _.shuffle function of Underscore.js library, which shuffles the list of data with Fisher-Yates Shuffle algorithm.

function getRandomNumber() {
    var rand, index = 0, shuffled = [1, 2, 3, 4, 5, 6, 7, 8, 9];

    shuffled.forEach(function(value) {
        rand = Math.floor(Math.random() * ++index);
        shuffled[index - 1] = shuffled[rand];
        shuffled[rand] = value;
    });

    return shuffled.reduce(function(result, current) {
        return result * 10 + current;
    }, 0);
}

console.log(getRandomNumber());

This program will always return a number which has all the 9 numbers in it and the length is also 9.

edited Apr 04 '14 at 05:35

answered Mar 28 '14 at 08:29

thefourtheye

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Technically I don't think this is Fisher-Yates, as this does not shuffle in place. – Peter Mar 28 '14 at 08:39
@Peter You are correct, I updated the answer now, please check :) – thefourtheye Mar 28 '14 at 08:51

score 1 · Answer 3 · answered Mar 28 '14 at 09:14

Recurse!

var randomize = function (str) {
    if (str.length == 9) return str;
    var newDigit = Math.floor(Math.random()*9 + 1);
    if (str.indexOf(newDigit) == -1) {
        return randomize(str + newDigit);
    } else {
        return randomize(str);
    }
}

There's a lot of room for optimisation there. Or just use a simple loop.

Working fiddle

Generate random integer with ALL digits from 1-9

3 Answers3