Java 程序查找一副牌中四张牌的组合数等于 24

Question

我有一个 Java 程序，它将获取一副纸牌并计算四张纸牌的组合数量等于 24。到目前为止，我有这个:

public class Assign5b {
    public static void main(String[] args) {
        int[] deck = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 
            1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 
            1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 
            1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13};

        int total;
        total = calculate(deck);
        output(total);
    }

    public static int calculate(int[] deck) {
        int total = 0;
        int stack1, stack2, stack3, stack4, accumulate;

        for (stack1 = 0; stack1 < 52; stack1++) {
            for (stack2 = (stack1 + 1); stack2 < 52; stack2++) {
                for (stack3 = (stack2 + 1); stack3 < 52; stack3++) {
                    for (stack4 = (stack3 + 1); stack4 < 52; stack4++) {
                        accumulate = (deck[stack1] + deck[stack2] + deck[stack3] + deck[stack4]);
                        if (accumulate == 24)
                            total++;
                    }
                }
            }
        }       
        return total;
    }   

    public static void output(int total){
        System.out.println ("The total number of card combinations of 4 that \n" + "equal 24 is: " + total);
    }
}

所以我的问题不是它不运行，或者它没有显示正确的值，而是那些嵌套循环。我不希望他们在那里。这使它运行效率非常低，我知道有更好的方法让它运行，但我只是无法想象它。

Answer 1

您可以在每个循环的开头添加检查，以查看运行总数是否已超过 24。在这种情况下，无论如何执行这些循环都是没有意义的:

public static int calculate(int[] deck, int target) {
    int total = 0;
    int stack1, stack2, stack3, stack4, accumulate;

    for (stack1 = 0; stack1 < 52; stack1++) {
        if (deck[stack1] > target) break;

        for (stack2 = (stack1 + 1); stack2 < 52; stack2++) {
            if (deck[stack1] + deck[stack2] > target) break;

            for (stack3 = (stack2 + 1); stack3 < 52; stack3++) {
                if (deck[stack1] + deck[stack2] + deck[stack3] > target) break;

                for (stack4 = (stack3 + 1); stack4 < 52; stack4++) {
                    if (deck[stack1] + deck[stack2] + deck[stack3] + deck[stack4] > target) break;
                    accumulate = (deck[stack1] + deck[stack2] + deck[stack3] + deck[stack4]);
                    if (accumulate == 24)
                        total++;
                }
            }
        }
    }

    return total;
}

这假设您的牌组按升序顺序排序，例如

int[] deck = {1, 1, 1, 1,
              2, 2, 2, 2,
              ...
              13, 13, 13, 13};