The following is my implementation of Selection Sort:
package algorithm.selectionsort;
public class SelectionSort {
public static void main(String[] args) {
int[] myArray = selectionSort(new int[] { 9, 9, 9, 8, 7, 73, 32, 109, 1100, 432, 321, 0 });
for (int element : myArray) {
System.out.print("" + element + " ");
}
}
public static int[] selectionSort(int[] a) {
int min;
for (int i = 0; i < a.length - 1; i++) {
min = i;
for (int j = i + 1; j < a.length; j++) {
if (a[j] < a[min]) {
min = j;
int temp = a[i];
a[i] = a[min];
a[min] = temp;
}
}
}
return a;
}
}
I noticed that my instructor codes it slightly differently:
public static int[] selectionSort(int[] a) {
int min;
for (int i = 0; i < a.length - 1; i++) {
min = i;
for (int j = i + 1; j < a.length; j++) {
if (a[j] < a[min]) {
min = j;
}
}
int temp = a[i];
a[i] = a[min];
a[min] = temp;
}
return a;
}
Both implementations work. I'm curious as to what the difference here is. Is it efficiency?
The difference between your instructor's and yours is that he iterate through the array and for each element, search for the minimum, then perform a swap with the element after the wall index.
For yours, you iterate through the array and for each element, while searching for the minimum, if current value is < then the current tentative min, perform a swap with the element after the wall index.
So instead of swapping n times, you could possible swap n*n times for worst case:
Your swap for just one pass (worst case):
100, 90, 88, 70, 55, 43, 32, 28, 19, 10
90, 100, 88, 70, 55, 43, 32, 28, 19, 10
88, 100, 90, 70, 55, 43, 32, 28, 19, 10
70, 100, 90, 88, 55, 43, 32, 28, 19, 10
55, 100, 90, 88, 70, 43, 32, 28, 19, 10
43, 100, 90, 88, 70, 55, 32, 28, 19, 10
32, 100, 90, 88, 70, 55, 43, 28, 19, 10
28, 100, 90, 88, 70, 55, 43, 32, 19, 10
19, 100, 90, 88, 70, 55, 43, 32, 28, 10
10, 100, 90, 88, 70, 55, 43, 32, 28, 19
Your instructor's swap for just one pass (worst case):
100, 90, 88, 70, 55, 43, 32, 28, 19, 10
10, 90, 88, 70, 55, 43, 32, 28, 19, 100
In essence, you swap the values while in the midst of searching for the min. The "min" you swapped may not be the lowest value in the array.