如何在二维数组的随机位置中放置一定数量的整数？

Question

I'm trying to put a certain amount of integers into an array in random spots without putting them in the same place.

My combine method concatenates two given integers and returns the Int. Places is an arrayList to keep the locations of the integers already put into the array. The random method returns a random integer in between the two given ints.

The combine method works and so does the random method, but I'm not sure why it isn't working.

public void fillOne(int b)
{
    for(int x = 0; x < b; x++)
    {
        int kachow = random(0, 5);
        int kachigga = random(0, 5);
        int skrrt = combine(kachow, kachigga);
        if(notInArray(skrrt))
        {
            locations[kachow][kachigga] = 1;
            places.add(skrrt);
        }
    }
}

Answer 1

You haven't really explained what isn't working. But an obvious flaw in your algorithm is that it isn't guaranteed to set b elements to 1 . If your algorithm generates a duplicate position then it will set fewer than b elements.

Your logic for storing the combined positions is overly complex. One solution would be to reverse the logic: generate a single integer representing both dimensions then divide it into two when you are setting the location. That makes the checks a lot simpler.

For example, if your array is 5x5:

Set<Integer> positions = new HashSet<>();
while (positions.size() < n)
    positions.add(random.nextInt(25));
for (int p: positions)
    locations[p/5][p%5] = 1;

Because positions is a set it automatically excludes duplicates which means the code will keep adding random positions until their are n distinct positions in the set.

Even simpler, if you are using Java 8:

random.ints(0, 25)
    .distinct().limit(n)
    .forEach(p -> locations[p/5][p%5] = 1);