Created
September 20, 2016 15:20
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Quick select algorithm searching for median in array
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public class QuickSelect { | |
public static void main(String[] args) { | |
Scanner scanner = new Scanner(System.in); | |
int n = scanner.nextInt(); | |
int[] array = new int[n]; | |
for (int i = 0; i < array.length; i++) { | |
array[i] = scanner.nextInt(); | |
} | |
int pos = array.length / 2; | |
int median = quickSelect(array, pos, 0, array.length - 1); | |
System.out.print(median); | |
} | |
private static int quickSelect(int[] array, int pos, int left, int right) { | |
if (left == right && left == pos) { | |
return array[left]; | |
} | |
int posRes = partition(array, left, right, pos); | |
if (posRes == pos) { | |
return array[posRes]; | |
} else if (posRes < pos) { | |
return quickSelect(array, pos, posRes + 1, right); | |
} else { | |
return quickSelect(array, pos, left, posRes - 1); | |
} | |
} | |
private static int partition(int[] array, int left, int right, int pos) { | |
int pivot = array[left]; | |
int position = left; | |
for (int i = left + 1; i <= right; i++) { | |
if (array[i] <= pivot) { | |
position++; | |
swap(array, i, position); | |
} | |
} | |
swap(array, left, position); | |
return position; | |
} | |
private static void swap(int[] array, int first, int second) { | |
int temp = array[first]; | |
array[first] = array[second]; | |
array[second] = temp; | |
} | |
} |
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How about length of the array is even?