Finding min and max value in each column in array

Question

I have a problem with my program. I want to print min and max in each column but It doesn't work properly. I think everything should be ok. When the loop comes to end I restart min and max value.

public class tablice2 {
  public static void main(String[] args){
      int t [][] = new int [5][5];
      int n [] = new int [5];
      int x [] = new int [5];
      Random r = new Random();
      int min  = t[0][0];
      int max = t[0][0];


      for (int i = 0; i <t.length ;i++){
          min = 0;
          max = 0;
          for(int j = 0; j < t[i].length ;j++){
            t[i][j] = r.nextInt(6)-5;
              System.out.print(t[i][j] + " ");

              if (t[j][i] < min){
                  min = t[j][i];
              }

              if (t[j][i] > max){
                  max = t[j][i];
              }

          }
          n[i]=min;
          x[i]=max;


          System.out.println(" ");
      }

      for(int p=0;p<x.length;p++){
          System.out.println("Max Column "+p + ": " +x[p] );
      }

      for(int k=0;k<n.length;k++){
          System.out.println("Min Column "+k + ": " +n[k]);
      }



  }
}

Answer 1

You have initialized min as zero, I'd suggest Integer.MIN_VALUE . Otherwise positive values cannot be "found".

This is also the kind of problem that somebody has already solved for you, eg via streams:

assertThat(
        IntStream.of(new int[] { 1, 2, 3, 4, 5 }).max().getAsInt(), 
        is(5));

Answer 2

Do not input and sort at the same time as the elements may still be initialized with the default values (ie 0 ). Also, in the outer loop, reset max and min to the first element of the column.

Do it as follows:

import java.util.Random;

public class Main {
    public static void main(String[] args) {
        int t[][] = new int[5][5];
        int n[] = new int[5];
        int x[] = new int[5];
        Random r = new Random();
        int min;
        int max;

        for (int i = 0; i < t.length; i++) {
            for (int j = 0; j < t[i].length; j++) {
                t[i][j] = r.nextInt(10) - 5;
                System.out.printf("%4d", t[i][j]);
            }
            System.out.println();
        }

        for (int i = 0; i < t.length; i++) {
            min = t[0][i];
            max = t[0][i];
            for (int j = 0; j < t[i].length; j++) {
                if (t[j][i] < min) {
                    min = t[j][i];
                }
                if (t[j][i] > max) {
                    max = t[j][i];
                }
            }
            n[i] = min;
            x[i] = max;
        }

        for (int p = 0; p < x.length; p++) {
            System.out.println("Max Column " + p + ": " + x[p]);
        }

        for (int k = 0; k < n.length; k++) {
            System.out.println("Min Column " + k + ": " + n[k]);
        }
    }
}

A sample run:

   3  -4   2   0   1
  -2  -2   4  -1  -2
  -3   1   4  -1   0
  -4   4  -2  -5   2
  -5  -3  -3  -4  -1
Max Column 0: 3
Max Column 1: 4
Max Column 2: 4
Max Column 3: 0
Max Column 4: 2
Min Column 0: -5
Min Column 1: -4
Min Column 2: -3
Min Column 3: -5
Min Column 4: -2

Notes:

1. I have changed r.nextInt(6)-5 to r.nextInt(10) - 5 in order to produce a mix of negative, 0 and positive numbers so that you can quickly validate the result. You can change it back to r.nextInt(6)-5 as per your requirement.
2. I have also used printf instead of print to print each number with a space of 4 units. You can change it back to print if you wish so.
3. Use of Integer.MAX_VALUE and/or Integer.MIN_VALUE is not required at all to solve this problem.

Feel free to comment in case of any doubt.

Answer 3

您的第一个循环必须在列（j）上。

t[0].length

Answer 4

First in loop set your min to min = Integer.MAX_VALUE and similarly with max = Integer.MIN_VALUE . That will provide us that every random number will be (at least) smaller than initialized min (and similar for max)

In this case, you are draw numbers from -5 to 0 so you can set min as for example -6 and max 1 and then you are sure the drawed number will be higher than -6 and less than 1 and will update correctly

In your code you mixed i and j - it should be

if (t[i][j] < min){
    min = t[i][j];
}

and similarly in the rest of the code

Also when you create an array in Java it is automatically initialized with 0's. So

int t [][] = new int [5][5];
int min  = t[0][0];

means min = 0 because all array is filled by 0's so you don't have to duplicate your code