Finding minimum and maximum in Java 2D array

问题:

I have been trying to figure this out for a while and need some help. I need to find the min/max values and print them out for a multidimensional array. Here are the two ways that I have tried.

import java.util.*;

class MinMax {
    public static void main(String[] args) {
        int[][] data = {{3, 2, 5},
                {1, 4, 4, 8, 13},
                {9, 1, 0, 2},
                {0, 2, 6, 3, -1, -8}};
        Arrays.sort(data);
        System.out.println("Minimum = " + data[0]);
        System.out.println("Maximum = " + data[data.length - 1]);
    }
}

This version complies but doesn't run.

import java.util.*;

class MinMax {
    public static void main(String[] args) {
        int[][] data = {{3, 2, 5},
                {1, 4, 4, 8, 13},
                {9, 1, 0, 2},
                {0, 2, 6, 3, -1, -8}};

    public static int getMaxValue(int[] numbers) {
        int maxValue = numbers[0];
        for (int i = 1; i < numbers.length; i++) {
            if (numbers[i] > maxValue) {
                maxValue = numbers[i];
            }
            return maxValue;
            {
                public static int getMinValue (int[] numbers) {
                    int minValue = numbers[0];
                    for (int i = 1; i < numbers.length; i++) {
                        if (numbers[i] < minValue) {
                            minValue = numbers[i];
                        }
                    }
                return minValue;
            }

This version just throws me a bunch of errors in compiling. Any help is greatly appreciated.

回答1:

Ok, I've kinda fixed your code. Actually your mistake was that you have not been traversing all the cells of your multidimensional array.

So, I've added additional loop into getMinValue/getMinValue methods and fixed array elements addressing.

import java.util.*;

class MinMax {
    public static void main(String[] args) {
        int[][] data = {
                {3, 2, 5},
                {1, 4, 4, 8, 13},
                {9, 1, 0, 2},
                {0, 2, 6, 3, -1, -8}
        };
        System.out.println(getMaxValue(data));
        System.out.println(getMinValue(data));
    }


    public static int getMaxValue(int[][] numbers) {
        int maxValue = numbers[0][0];
        for (int j = 0; j < numbers.length; j++) {
            for (int i = 0; i < numbers[j].length; i++) {
                if (numbers[j][i] > maxValue) {
                    maxValue = numbers[j][i];
                }
            }
        }
        return maxValue;
    }

    public static int getMinValue(int[][] numbers) {
        int minValue = numbers[0][0];
        for (int j = 0; j < numbers.length; j++) {
            for (int i = 0; i < numbers[j].length; i++) {
                if (numbers[j][i] < minValue ) {
                    minValue = numbers[j][i];
                }
            }
        }
        return minValue ;
    }
}

回答2:

I have a more fun solution using Java 8 :)

IntSummaryStatistics stats = Arrays.stream(data).flatMapToInt(Arrays::stream).collect(Collectors.summarizingInt(Integer::intValue));
int max = stats.getMax();
int min = stats.getMin();

It's a different solution than yours, obviously. But it does the same thing. To begin with, we convert the 2D array into a Stream of ints. In order to do this first we need to call flatMapToInt. We do this to stream all the elements in the array in a flat way. Imagine if we just start using a single index to iterate over the whole 2D array. It's something like that. Once we have converted the array into a stream, we will use IntSummaryStatistics in order to reuse the same stream for both min and max.

回答3:

Your problem is: You are sorting the array of int arrays instead of sorting each individual int in each int array.

To solve this: Loop through each int array in the array of int arrays.

Instructions for finding the maximum and minimum of a 2D int array using Arrays.sort():

1. Declare a 2D int array to sort called data.
2. Declare two ints, one to hold the maximum value, the other the minimum value.
   • The initial value of the maximum should be Integer.MIN_VALUE and the initial value of the minimum should be Integer.MAX_VALUE to make sure that negative values are handled.
3. Loop through data from 0 to data.length:
   1. Sort data[i]
   2. Check if the first value of data[i] is less than the minimum and change it if it is.
   3. Check if the last value of data[i] is greater than the maximum and change it if it is.
4. Output your result.

Example:

import java.util.Arrays;

public class Main {
    public static void main(String[] args) {
        int[][] data = {{3, 2, 5},
            {1, 4, 4, 8, 13},
            {9, 1, 0, 2},
            {0, 2, 6, 3, -1, -8} };

        int maximum = Integer.MIN_VALUE;
        int minimum = Integer.MAX_VALUE;

        for(int i = 0; i < data.length; i++) {
            Arrays.sort(data[i]);

            if(data[i][0] < minimum) minimum = data[i][0];
            if(data[i][data[i].length - 1] > maximum) maximum = data[i][data[i].length - 1];
        }

        System.out.println("Minimum = " + maximum);  
        System.out.println("Maximum = " + minimum); 
    }
}

回答4:

package array;

public class Max_number {

// 2 5 7 9
// 3 6 8 1

public static void main (String []arg) {

    int a[][] = {{2,5,7,9},{3,6,8,1}};
    int max=a[0][0];
    for (int i=0; i<2; i++) //row
    {
        for (int j=0; j<4; j++) //coloum
        {
            if(a[i][j]>max)
            {
                max=a[i][j];
        }

    }

}
    System.out.println("maximum number is"+max);
}

}