用户提供的整数数组的第一，第二和第三大数

Question

In this program, size of array and array elements are taken from user.

This code passes all the cases I have tried but not able to pass, where size of array is 4 and elements are {5,5,5,2}

Here output should be 5 5 5
But I am getting 2 2 5

I am able to figure out the problem is in this part.

else if((max1 == max2 && max2 == max3 && max1 == max3) && x[i] < max2)
                {
                    max2 = x[i];
                    if(max2 < max3)
                    {
                        max3 = max2;
                    }
                }

How can I solve this problem using array only. Don't need solution in collections.

import java.util.*;
    class ThirdLargest 
    {
        public static void main(String[] args) 
        {
            Scanner sc = new Scanner(System.in);
            System.out.println("Enter size for array: ");
            int size = sc.nextInt();
            int[] x = new int[size];
            for(int i = 0; i < x.length; i++)
            {
                System.out.println("Enter elements for array: ");
                x[i] = sc.nextInt();
            }
            System.out.println("Array is: ");
            for(int i = 0; i < x.length; i++)
            {
                System.out.print(x[i] +"    ");
            }
            System.out.println();
            if (x.length >= 3)
            {
                int max1 = x[0], max2 = x[0], max3 = x[0];
            for (int i = 1; i < x.length; i++)
            {
                    if(x[i] > max1)
                    {
                        max3 = max2;
                        max2 = max1;
                        max1 = x[i];
                    }
                    else if(x[i] > max2)
                    {
                        max3 = max2;
                        max2 = x[i];
                    }
                    else if (x[i] > max3)
                    {
                        max3 = x[i];
                    }
                    else if((max1 == max2 && max2 == max3 && max1 == max3) && x[i] < max2)
                    {
                        max2 = x[i];
                        if(max2 < max3)
                        {
                            max3 = max2;
                        }
                    }
                    else if(max2 == max3 && x[i] < max3)
                        {
                            max3 = x[i];
                        }
                }
            System.out.println("3rd, 2nd and 1st maximum: " + max3 +"   "+max2+"    "+max1);
            }
            else
            {
                System.out.println("Array size is short");      
            }       
        }
    }

Answer 1

This code is not human readable, you will stuck in this for hours trying to debug. First, you need to split this code to methods, don't try to do all thing in one method. You need to decouple logic of receiving int array from user from logic that doing max values calculation. Example:

public int[] threeMaximumValuesFrom(int[] array) {
    int[] sorted = sortArray(array);
    int[] result = {
        sorted[array.length - 1];
        sorted[array.length - 2];
        sorted[array.length - 3];
    }
    return result;
}

private int[] sortArray(int[] array) {
    //when you don't want to use jdk sort implement your own
    //in any way other parts of code should knows nothing about it
    Arrays.sort(array);
    return array;
}

Answer 2

The problem is that repeated integers in the array are not kept track of as unique elements.

When you look at the array x = [5, 5, 5, 2] on paper you can see that there are three unique int elements of value 5 so the three largest should be 5, 5, 5 but the way the tests are now, when it reaches the value 2 at the end of the array, it doesn't know that max3 , max2 , and max1 each represent three distinct ints of value 5 for x[0] , x[1] , and x[2] .

The problem can be seen here in this code section:

...

else if ((max1 == max2 && max2 == max3 && max1 == max3) && x[i] < max2) {
    max2 = x[i];
    if (max2 < max3) {
        max3 = max2;
    }
} else if (max2 == max3 && x[i] < max3) {
    max3 = x[i];
}

...

It doesn't work for two reasons:

1. In the first if/else block, both max2 and max3 are changed so the other if/else blocks will work during future loop iterations, but the problem is that this assumes there will be a next iteration . It does not work when the code block above is the last thing executed in the loop, eg [5, 5, 5, 2 ].

   • (side note) if max1 , max2 , and max3 are all equal, and x[i] < max2 , then after the line:

      max2 = x[i]; 

     max2 will always be less than max3 so the test if (max2 < max3) { is not needed.

2. The tests max1 == max2 && max2 == max3 && max1 == max3 and max2 == max3 do not handle the cases where:

   • max1 , max2 , and max3 are all equal, but each represents a different element in the array, eg [5, 5, 5, 2] , when i = 3 in the for loop then max1 could represent x[0] , max2 could represent x[1] , and max3 could represent x[2] but because uniques are not kept track of, max2 and max3 are reassigned to 2 and because this is the last thing the for loop executes, the output is 2, 2, 5 .

   • max2 and max3 are equal but each represents a different element in the array, eg for [7, 7, 8, 2] , when i = 3 in the for loop, max2 represents x[0] and max3 represents x[1] but again, because uniques are not kept track of, max3 is reassigned to 2 and the output is 2, 7, 8 instead of 7, 7, 8 .

To be clear:

• If you tested the array [5, 5, 5, 5, 2] where the 2 occurs at index 4 , the program would output 2, 2, 5 because of the reasons mentioned above.
• If you tested the array [5, 5, 5, 2, 5] where the 2 occurs at index 3 , the program would output 2, 5, 5 because there is only one 5 that appears after the 2 .
• If you tested the array [5, 5, 2, 5, 5] where the 2 occurs at index 2 , the program would output 5, 5, 5 because there are two 5s that occur after the 2 . In the end: max1 , max2 , and max3 all equal each other, 5 .
• If you tested the array [5, 5, 2, 5, 5, 3] which is just the previous array but with 3 added at the end, then the program would output 3, 3, 5 because when i = 5 in the for loop, max1 , max2 , and max3 all equal each other, 5 , and the program assumes this is because they were all initially set to x[0] .

Now that you understand why the program does not work, I believe a better way to solve this problem would be to first initialize max1 , max2 , and max3 to the lowest possible value using the Integer wrapper class, read about it here :

Replace

int max1 = x[0], max2 = x[0], max3 = x[0];

with

int max1, max2, max3;
max1 = max2 = max3 = Integer.MIN_VALUE;

then change the last for loop to begin at index 0 now instead of 1

for (int i = 0; i < x.length; i++) {

and delete the last two if/else blocks:

else if ((max1 == max2 && max2 == max3 && max1 == max3) && x[i] < max2) {
    max2 = x[i];
    if (max2 < max3) {
        max3 = max2;
    }
} else if (max2 == max3 && x[i] < max3) {
    max3 = x[i];
}

You were very close to solving it and only a few small changes are needed to fix the bugs.

Hope this was helpful, and cheers!

Answer 3

int[] numbers = {5, 5, 5, 2};
Arrays.stream(numbers).sorted().skip(numbers.length - 3).forEach(System.out::println);

We make stream out of your array, then we sort it, we skip arrayLength - n elements (n represents how many max numbers you want to print out) and we print each one of the numbers that are left.