使用随机生成的值检查数组中的重复项

Question

I'm working on exercism question and am stuck on one of the jasmine-node based tests, which says that I should be able to generate 10000 random names without any clashes (eg 2 randomly generated names match). This is the test:

it('there can be lots of robots with different names each', function() {

    var i,
    numRobots = 10000,
    usedNames = {};

    for (i = 0; i < numRobots; i++) {
      var newRobot = new Robot();
      usedNames[newRobot.name] = true;
    }

    expect(Object.keys(usedNames).length).toEqual(numRobots);

});

What I think I need to do is:

1. Create an array to hold all the names (robotNames),
2. Each time a name is generated, check if it exists in the array,
3. If it does, generate another name,
4. If it doesn't, add it to the array.

And here is my code so far...

"use strict";

var robotNames = [];
var name;

var Robot = function() {
    this.name = this.generateName();
};

Robot.prototype.generateName = function() {

    var letters = "";
    var alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

    var numbers = "";
    var digits = "0123456789";

    // generate random characters for robot name...

    for( var i=0; i < 2; i++ ) {
        letters += alphabet.charAt(Math.floor(Math.random() *    alphabet.length));
    };

    for( var i=0; i < 3; i++ ) {
        numbers += digits.charAt(Math.floor(Math.random() * digits.length));
    };

    name = letters+numbers;

    // Loop through array to check for duplicates

    for(var i = 0; i < robotNames.length; i++) {
        if (name == robotNames[i]) {
            this.generateName();
            return;
        } else {
            robotNames.push(name);
        }
    }

    return name;
};

Robot.prototype.reset = function() {
     this.name = this.generateName();
};

module.exports = Robot;

The test fails with an error message: "Expected 9924 to equal 10000."

The '9924' number is slightly different each time I run the test. I'm thinking this means the generateName function is eventually generating 2 matching random names. It seems as though my loop for checking duplicates is not being run and I'm not sure why.

I have tried a couple of different versions of the loop but with no success. So my questions is a) is my approach correct and there is something wrong with the syntax of my loop? or b) have I got the wrong idea about how to check for duplicates here?

Any pointers appreciated, thanks.

Answer 1

The problem is in this bit:

for(var i = 0; i < robotNames.length; i++) {
    if (name == robotNames[i]) {
        this.generateName();
        return;
    } else {
        robotNames.push(name);
    }
}

...you probably only want to push your name if NONE of the names fail to match. Here you're adding it to the list as soon as you find ONE that doesn't match. You want something more like:

for(var i = 0; i < robotNames.length; i++) {
    if (name == robotNames[i]) {
        return this.generateName();
    }
}
robotNames.push(name);

(actually, combined with the fact that you weren't even returning the recursive call to this.generateName(), I'm not sure how your program could work...)

Answer 2

Find a library with an implementation for Sets. Collections.js is a good example.

One property of a set is that it doesn't have duplicates. So when you add a value to a set it will look for a duplicate and then add the value if no duplicate exists.