How to see if an array has 4 of the same values. Java

Question

I have a poker program and in that program I have method that checks if there is a four of kind in an array.

public boolean isFourOfAKind(Card[] arr){}

I change arr[] to an int array by grabbing each of the cards values, 2-14 and store them in a separate array. How do I check(efficiently) if 4 integers are the same in that array?

*NOTE: I am passing in an array of 7 cards

My Two Pair Method (From Requests)

   /*
     * Returns 0 if no two pairs
     *  else returns the highest card out of the two pairs, 
     *  if two hands have the same highest pair then further inspection is needed
     */
    public static int isTwoPair(Card[] arr){
        int hold[] = new int[5];
        int values[] = new int[arr.length];
        int max = 0;
        boolean total = false;
        for(int i=0;i<arr.length;i++){
            values[i] = arr[i].getValue();
        }
        for(int i = 0;i<values.length;i++){
            for(int j = 0;j<values.length;j++){
                if(i==j){
                    continue;
                }
                if(values[i]==values[j]){
                    if(values[i]>max){
                        max = values[i];
                    }
                    int hold1 =0;
                    int hold2=0;

                    hold1 = j;
                    hold2=i;
                    int counter = 0;
                    for(int ii = 0;ii<values.length;ii++){
                        if(ii==j||ii==i){
                            continue;
                        }
                        hold[counter] = values[ii];
                        counter++;

                    }
                    //                     for(int iii: hold){
                    //                     System.out.print(" , "+ iii);
                    //                     }
                    //                     System.out.println();
                    if(isPair(hold)==0){
                        max = 0;
                        total = false;
                    }else{
                        int holdInt = isPair(hold);
                        if(holdInt>max){
                            max = holdInt;
                        }
                        total = true;
                    }
                }
            }
        }
        return max;

    }

How do you check two of a Kind? – dognose Nov 03 '15 at 23:32 — dognose, Nov 03 '15 at 23:32

Iłya Bursov · Answer 1 · 2015-11-03T23:34:11.143

2

I'd prefer to do it like this:

public boolean isFourOfAKind(Card[] arr){
    int[] counts = new int[15];
    for (Card c: arr) {
        counts[c.cardNum]++;
        if (counts[c.nameOfTheFieldWithCardNumber] == 4) return true;
    }
    return false;
}

also you can easily modify this method to check 2/3 of a kind/full house combinations

edited Nov 03 '15 at 23:34

answered Nov 03 '15 at 23:32

Iłya Bursov

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I didn't even consider this. This is a great method. – bpgeck Nov 03 '15 at 23:33
That's a good general-purpose method. If you can live with the restriction that you will always and only be evaluating 5-card hands, you can save considerable time by just using direct comparison and early return. – Lee Daniel Crocker Nov 03 '15 at 23:40
@LeeDanielCrocker can you post optimized solution for 5-card hand? – Iłya Bursov Nov 03 '15 at 23:42
I am dealing with a 7 card array – Sam Liokumovich Nov 05 '15 at 05:05

score 0 · Answer 2 · answered Nov 03 '15 at 23:57

If you sort the array by rank (2,3,...,King,Ace) then the following checks all become a lot easier:

Straight flush (incrementing rank, combined with Flush check)
Four of a kind (4 of the same rank grouped together)
Full house (first 2 are equal and last 2 are equal and middle is equal to one of them)
Straight (incrementing rank)
Three of a kind (3 of the same rank grouped together)
Two pair (2 groups of same rank)
One pair (2 of the same rank grouped together)
High card (last card)

The only one that doesn't benefit, is Flush, and checking for that doesn't require any sorting, so that's not a problem.

How to see if an array has 4 of the same values. Java

2 Answers2