## Monday, 16 November 2015

### Selection Sort in Java

Selection Sort

The selection sort is a combination of searching and sorting.

During each pass, the unsorted element with the smallest (or largest) value is moved to its proper position in the array. The number of times the sort passes through the array is one less than the number of items in the array.

The algorithm divides the input list into two parts:

1.Sublist of items already sorted, which is built up from left to right at the front (left) of the list, and

2. Sublist of items remaining to be sorted that occupy the rest of the list.

Steps:

Initially, the sorted sublist is empty and the unsorted sublist is the entire input list.

1. Find the smallest/largest (depending on sorting order) element in the unsorted sublist.

2. Exchanging (swapping) it with the leftmost unsorted element (putting it in sorted order).

3. Moving the sorted sublist boundaries one element to the right.

4. Repeat steps 3 and 4.

Example:

This is the initial, starting state of the array
Where the initial sorted left sublist is empty.

65 38 22 25 14

14 65 38 22 25 // sorted sublist = {14}

14 22 65 38 25 // sorted sublist = {14, 22}

14 22 25 65 38 // sorted sublist = {14, 22, 25}

14 22 25 38 65 // sorted sublist = {14, 22, 25, 38}

14 22 25 38 65 // sorted sublist = {14, 22, 25, 38, 65}

SelectionSort.java

public class SelectionSort {
public static void main(String[] args) {
int[] array = {64, 25, 12, 22, 11};
SelectionSort.sort(array);
SelectionSort.printArr(array);
}
private static void sort(int array[]) {
int n = array.length;
int idx,idxSorted;
// idxSorted: List sorted till this index

int iMin; // Min element index.

for (idxSorted = 0; idxSorted < n-1; idxSorted++) {
/* find the min element in the unsorted array[j .. n-1] */

/**Min index is the first element of unsorted list(default)*/
iMin = idxSorted;

for ( idx = idxSorted+1; idx < n; idx++) {
/**
* Find minimum element index in Unsorted List.
* Update the Minimum element index.
*/
if (array[idx] < array[iMin]) {
iMin = idx;
}
}

if(iMin != idxSorted) {
/** swap(array[j]<-->array[iMin]) */
int temp = array[idxSorted];
array[idxSorted] = array[iMin];
array[iMin] = temp;
}
}
}

private static void printArr(int[] array) {
StringBuffer sb = new StringBuffer();
for (int i : array) {
sb.append(i).append(" ");
}
System.out.println(sb.toString());
}
}
Output:
11 12 22 25 64