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Quick Sort with Randomized Partition
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package com.hrishikeshmishra.practices.sort; | |
import java.util.Arrays; | |
import java.util.concurrent.ThreadLocalRandom; | |
/** | |
* Problem: | |
* Quick Sort with Randomized Partition | |
* ; | |
* Algorithm: | |
* - Same as quick partition but, | |
* - Before partitioning swap one random index | |
* | |
* @author hrishikesh.mishra | |
* @link http://hrishikeshmishra.com/quick-sort-randomized-partition/ | |
*/ | |
public class QuickSortWithRandomizedPartition { | |
public static void sort(int[] array) { | |
sortHelper(array, 0, array.length - 1); | |
} | |
private static void sortHelper(int[] array, int p, int r) { | |
if (p < r) { | |
int q = randomizedPartition(array, p, r); | |
sortHelper(array, p, q - 1); | |
sortHelper(array, q + 1, r); | |
} | |
} | |
private static int randomizedPartition(int[] array, int p, int r) { | |
int randomIndex = ThreadLocalRandom.current().nextInt(p, r + 1); | |
swap(array, randomIndex, r); | |
return partition(array, p, r); | |
} | |
private static int partition(int[] array, int p, int r) { | |
int i = p - 1; | |
int j = p; | |
while (j < r) { | |
if (array[j] <= array[r]) { | |
swap(array, i + 1, j); | |
i++; | |
} | |
j++; | |
} | |
swap(array, i + 1, r); | |
return i + 1; | |
} | |
private static void swap(int[] array, int i, int j) { | |
int temp = array[i]; | |
array[i] = array[j]; | |
array[j] = temp; | |
} | |
} | |
class QuickSortWithRandomizedPartitionTest { | |
public static void main(String[] args) { | |
int[] array = {2, 8, 7, 1, 3, 5, 6, 4}; | |
System.out.println("Before Array: " + Arrays.toString(array)); | |
QuickSortWithRandomizedPartition.sort(array); | |
System.out.println("After Array: " + Arrays.toString(array)); | |
} | |
} |
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