Find missing numbers in array of sorted consecutive natural numbers [n,n+1, n+2, ... n + m] Objective-C

gistfile1.txt

#import <Foundation/Foundation.h>
#import <Cocoa/Cocoa.h>

NSArray *missingNumbers(NSArray *a){
	if(a.count < 2){
		return [NSArray new];
	}
	
	NSMutableArray *array = [NSMutableArray new];
	for (NSInteger i = 0; i < a.count - 1; i ++) {
		NSNumber *x = a[i];
		NSNumber *y = a[i+1];
		
		NSInteger xInt = [x integerValue];
		NSInteger yInt = [y integerValue];
		
		NSInteger diff = yInt - xInt;
		
		if(diff > 1){
			for (NSInteger i = xInt + 1; i < yInt; i++) {
				[array addObject:@(i)];
			}
		}
	}
	return array;
}

int main(int argc, char *argv[]) {
	@autoreleasepool {
		NSArray *a = @[@1,@3,@5];
		NSArray *r = missingNumbers(a);
		NSArray *e = @[@2,@4];
		NSCAssert([r isEqualToArray:e],@"");
		
		a = @[@2,@5];
		r = missingNumbers(a);
		e = @[@3,@4];
		NSCAssert([r isEqualToArray:e],@"");
		
		a = @[@10,@20];
	    r = missingNumbers(a);
		e = @[@11,@12,@13,@14,@15,@16,@17,@18,@19];
		NSCAssert([r isEqualToArray:e],@"");
		
		a = @[@99,@101,@102,@104];
	 	r = missingNumbers(a);
		e = @[@100,@103];
		NSCAssert([r isEqualToArray:e],@"");
		
		a = @[@9,@11,@13,@16];
		r = missingNumbers(a);
		e = @[@10,@12,@14,@15];
		NSCAssert([r isEqualToArray:e],@"");
	}
}