CODEWITHSUNDEEP
javaarrayssortingselection-sort
Paul Anthony Morillo
Paul Anthony Morillo

Reputation: 133

trying to implement selection sort but it wont work

i'm currently working on a project where I implement different types of sorting methods to sort an array. I got this implementation from my class but for some reason it is not working. I'm not sure where its going wrong and any help would be greatly appreciated.

public static void selectionSort(int[] a) {
    int n = a.length;
    System.out.println(n);
    for (int i = 0; i < n - 1; i++) {
        int min = i;
        for (int j = i + 1; j < n; j++) {
            if (a[j] < a[min]) {
                int swap = a[i];
                a[i] = a[min];
                a[min] = swap;
            }
        }
    }
}

The Algorithm: Finds the minimum value in the list. Swaps it with the value in the first position. Repeat the steps above for the remainder of the list (starting at the second position and advancing each time). It divides the list into two parts. The sublistof items already sorted. The sublistof items remaining to be sorted.

input

int[] a = new int[]{-2, 4, 8, 1, 9, -6};

expected output

-6, -2, 1, 4, 8, 9

Upvotes: 1

Views: 35

Answers (3)

Roshana Pitigala
Roshana Pitigala

Reputation: 8796

You could just use the java.util.Arrays class for this

int[] a = new int[]{-2, 4, 8, 1, 9, -6};
Arrays.sort(a);

this sorts the array a into ascending order (your expected output).

Java is pre-built with several tools. Always look for them, writing your own algorithm is fun, but it can be erroneous and painstaking.

Upvotes: 1

Roshana Pitigala
Roshana Pitigala

Reputation: 8796

The problem lies in the for loop, min and i variables.

int min = i; //min variable is useless, as min is always equals to i
for (int j = i + 1; j < n; j++) {
    if (a[j] < a[min]) {
        int swap = a[i];
        a[i] = a[min]; // remember min equals to i, so here you are assigning the same value
        a[min] = swap; // this should be a[j]
    }
}

Change the for loop

for (int j = i + 1; j < n; j++) {
    if (a[j] < a[i]) {
        int swap = a[i];
        a[i] = a[j];
        a[j] = swap;
    }
}

Upvotes: 1

Sumit Bhardwaj
Sumit Bhardwaj

Reputation: 81

You're missing a crucial step to update the minimum index here. Have a look at if block in below code.

public static void selectionSort(int[] a) {
    int n = a.length;
    for (int i = 0; i < n - 1; i++) {
        int min = i;
        for (int j = i + 1; j < n; j++) {
            if (a[j] < a[min]) {
                min = j;
                int swap = a[i];
                a[i] = a[min];
                a[min] = swap;
            }
        }
    }
}

Upvotes: 1

Related Questions