Random integer in a certain range excluding one number

Question

I would like get a random number in a range excluding one number (e.g. from 1 to 1000 exclude 577). I searched for a solution, but never solved my issue.

I want some

Answer 1

As @ebyrob suggested, you can create a function that makes a mapping from a smaller set to the larger set with excluded values by adding 1 for each value that it is larger than or equal to:

// min - integer
// max - integer
// exclusions - array of integers
//            - must contain unique integers between min & max
function RandomNumber(min, max, exclusions) {
    // As @Fabian pointed out, sorting is necessary 
    // We use concat to avoid mutating the original array
    // See: http://stackoverflow.com/questions/9592740/how-can-you-sort-an-array-without-mutating-the-original-array
    var exclusionsSorted = exclusions.concat().sort(function(a, b) {
        return a - b
    });

    var logicalMax = max - exclusionsSorted.length;
    var randomNumber = Math.floor(Math.random() * (logicalMax - min + 1)) + min;

    for(var i = 0; i < exclusionsSorted.length; i++) {
        if (randomNumber >= exclusionsSorted[i]) {
            randomNumber++;
        }
    }

    return randomNumber;
}

Example Fiddle

Also, I think @JesusCuesta's answer provides a simpler mapping and is better.

Update: My original answer had many issues with it.