#import <Foundation/Foundation.h>

@interface QuickSort: NSObject

- (NSArray *) quickSortArray:(NSArray *)unsortedArray;

@implementation QuickSort

- (NSArray *) quickSortArray:(NSArray *)unsortedArray {

// Time complexity: O(n^2).

// * First time arround is to separate the entire array.

// * Second time around should sort the rest of the array.

// Space complexity: O(log n) +1 for unsortedArray but the mutable copy never gets added to the autorelease pool.

// All of the arrays that are not attached to the returnArray are released by a compiler pass at the end of the method.

int count = (int)[unsortedArray count];

if (count <= 1) {

return unsortedArray;

}

int pivot = [[unsortedArray objectAtIndex: (count/2)] intValue];

NSMutableArray *smallerThanArray = [NSMutableArray array];

NSMutableArray *largerThanArray = [NSMutableArray array];

NSMutableArray *pivotArray = [NSMutableArray array];

[pivotArray addObject: @(pivot)];

for (int e = 0; e < count; e++) {

int num = [[unsortedArray objectAtIndex:e] intValue];

if (num < pivot) {

[smallerThanArray addObject: @(num)];

} else if (num > pivot) {

[largerThanArray addObject: @(num)];

// To address the possibly duplicate that is defined in the pivot, in this case 4.

} else if (e != (count/2) && pivot == num) {

[pivotArray addObject: @(num)];

}

}

NSMutableArray *returnArray = [NSMutableArray array];

[returnArray addObjectsFromArray: [self quickSortArray: smallerThanArray]];

[returnArray addObjectsFromArray: pivotArray];

[returnArray addObjectsFromArray: [self quickSortArray: largerThanArray]];

return returnArray;

}

int main(int argc, const char * argv[]) {

@autoreleasepool {

NSArray *quickSortData = @[@4, @3, @10, @44, @6, @4, @1, @7];

QuickSort *qs = [[QuickSort alloc] init];

NSArray *sortedNumbers = [qs quickSortArray:quickSortData];

NSLog(@"Sorted Numbers %@", sortedNumbers);

}

return 0;

}