Algorithm to verify if a two-dimensional array has two equals rows

Question

Define a method in which, given a two-dimensional array, evaluates if it has at least two identical rows

I've tried to come up with an algorithm to do it but I didn't go very far. This is what I got:

public static boolean righeUguali(int[][] a){
    boolean rUguali=false;

    for(int i=0; i<a.length; i++)
        for(int j=0; i<a[i].length; j++)
            if(Arrays.equals(a[i],a[j]))
                rUguali = true;
    return rUguali;

could you help me fix this code?

Answer 1

• You need to ensure that you are not comparing the row with itself. You ensure that by starting j with i+1
• Both loops need to iterate over the rows
• The fist of the two rows cannot be the last one, otherwise there would be no second row left to compare it to.
• optimization: you can terminate as soon as you found two equal rows

Here the modified code:

public static boolean righeUguali(int[][] a){
    for(int i=0; i<a.length-1; i++)
        for(int j=i+1; i<a.length; j++)
            if(Arrays.equals(a[i],a[j]))
                return true;
    return false;
}