How to solve HackerRank problems in Objective-C - objective-c

Question

Can anybody explain how to give the hacker rank test in objective-C. Specially the part "Read input from STDIN. Print output to STDOUT"
How to read input and out in objective-c ?
What i have got so far is get input like
NSFileHandle *fileHandler = [NSFileHandle fileHandleWithStandardInput];
NSData *inputData = [fileHandler availableData];
NSString *inputString = [[NSString alloc] initWithData:inputData encoding:NSUTF8StringEncoding];
But to print output, following does not print anything on HackerRank console (but works flawlessly on Xcode console)
NSFileHandle* fileHandler=[NSFileHandle fileHandleWithStandardOutput];
[fileHandler writeData: [formattedString dataUsingEncoding: NSNEXTSTEPStringEncoding]];

Answer 1

The simplest possible way to "Read input from STDIN. Print output to STDOUT" would be to use scanf and printf.
Here's a sample template to get you started:
#import <Foundation/Foundation.h>
int main (int argc, const char * argv[]) {
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
int count;
scanf("%d", &count);
NSMutableArray *inputIntegers = [NSMutableArray new];
for (int i=0; i<count; i++) {
int inputElement;
scanf("%d", &inputElement);
[inputIntegers addObject:[NSNumber numberWithInt:inputElement]];
}
//to print a specific element:
printf("printing element 0: %d", (int)[inputIntegers[0] integerValue]);
[pool drain];
return 0;
}
Before you take a shot at this journey, a few things:
Make sure ARC is disabled (search for CLANG_ENABLE_OBJC_ARC in build settings, and set it to NO)
Avoid using self. This is functional programming.
Use C functions, not Objective-C methods, meaning, use
instead of
- (NSInteger)sumOfNumbers : (NSInteger)a and:(NSInteger)b {
return a + b;
}
use
int sumOfNumbers(int a, int b){
return a + b;
}
Happy Programming.

Answer 2

Having just been handed one of these tests, I opted to get out of main.m immediately and into Objective-C like so:
#import <Foundation/Foundation.h>
//Objective-C helper class to take over from main.m
//.h
#interface MainClass : NSObject
+ (BOOL)startMain;
#end
//.m
#implementation MainClass
+ (BOOL)startMain {
//Read the STDIN here using the Objective-C wrapper methods
NSInteger n = [self readInt];
[self printInt:n];
NSArray *numbers = [self readIntArrayOfLength:n];
[self printIntNumberArray:numbers];
return YES;
}
+ (NSInteger)readInt {
int n;
scanf("%i",&n);
return n;
}
+ (NSArray *)readIntArrayOfLength:(NSInteger)len {
NSMutableArray *result = [NSMutableArray array];
for (int i =0; i < len; i++) {
[result addObject:[NSNumber numberWithInt:[self readInt]]];
}
return [result copy];
}
//Helpers to print an int and array of ints to STDOUT
+ (void)printInt:(NSInteger)i {
printf("%li\n",(long)i);
}
+ (void)printIntNumberArray:(NSArray *)array {
printf("[");
[array enumerateObjectsUsingBlock:^(NSNumber *n, NSUInteger idx, BOOL * _Nonnull stop) {
printf("%li",(long)[n integerValue]);
if (idx < array.count-1) {
printf(",");
}
}];
printf("]\n");
}
#end
//This is what will actually run when you hit "Run Code"
int main(int argc, char * argv[]) {
#autoreleasepool {
return [MainClass startMain];
}
}
Now you can do whatever you like from here using Objective-C.
So in this example a sample input of:
3
11 2 4
Would produce this output:
3
[11,2,4]
Not useful in of itself but illustrates the successful read.
It's a lot simpler in Swift, but here's code to accomplish the same thing anyway:
func readInt() -> Int? {
if let ln = readLine() {
return Int(ln)
}
return nil
}
func readIntArray() -> [Int]? {
if let ln = readLine() {
return ln.characters.split(" ").filter({ Int(String($0)) != nil }).map({ Int(String($0))! })
}
return nil
}
let n = readInt()!
let array = readIntArray()!
print(n)
print(array)
The functions return optionals because even though you are going to force-unwrap the input, better the crash for a nil optional happens in your code than the boilerplate.

Answer 3

#import <Foundation/Foundation.h>
int sum(int a, int b) {
return a + b;
}
int main() {
#autoreleasepool {
int T;
int A;
int B;
printf("Enter number of test cases: ");
scanf("%d", &T);
for (int i=0; i < T; i++) {
scanf("%d", &A);
scanf("%d", &B);
printf("%d\n", sum(A,B));
}
}
return 0;
}
That ought to do it.

Answer 4

Your question is really too general for SO, do not be surprised if it gets closed soon. You need in general to ask specific questions, show what you've tried, etc. But if you're just after a few hints to get you going...
You don't say whether you are a programmer already or know Objective-C in particular, assuming both:
In Xcode look at the Command Line Tool project type
Look into NSFileHandle and its methods, e.g. fileHandleWithStandardInput
Note you can also use the C stdio functions, converting C-style to Objective-C styles strings etc. as needed.

Answer 5

I created github repo with some hackerrank problem solutions written in objective-c. It is on the beginning stage, feel free to contribute by adding your solutions as well.
HackerRank for Objective-C

Answer 6

Since Objective-C is a superset of C, you can use C methods for reading and printing out:
NSInteger n;
char *input[25];
NSMutableArray *strings = [NSMutableArray array];
NSString *s;
NSString *temp;
scanf("%lu", &n);
for (NSInteger i = 0; i < n; ++i) {
scanf("%s", input);
s = [NSString stringWithUTF8String:input];
[inputs addObject:s];
}
If n is of type int, you can read it as:
scanf("%d", &n);