Question

This is more a curiosity question than a pressing one. This question is looking for a better way to do the following, meaning without using two for loops.

I have an NSArray *array of NSStrings and a method -(BOOL)isGoodString:(NSString *)string. I want to jump into the array at a random spot and find the first good string, wrapping around the end if necessary. However, it may be that there is no good string, so I need to know that as well. Here’s the current implementation:

-(NSString *)randomGoodString {
  int N = [array count]
  int start = arc4random() % N;
  for (int j=start; j<N ; ++j) {
    if isGoodString([array objectAtIndex:j]) {
      return [array objectAtIndex:j];
    }
  }
  for (j=0; j<start ; ++j) {
    if isGoodString([array objectAtIndex:j]) {
      return [array objectAtIndex:j];
    }
  }
  return @"";
}

Any suggestions? Efficiency would be nice, but since this really is more for curiosity, anything that works in finite time would be nice to hear about.

Answer 1

Eliminate your second search loop by using a modulus:

-(NSString *)randomGoodString {
  int N = [array count]
  int start = arc4random() % N;
  for (int j=0; j<N ; ++j) {
    index = (j+start)%N;
    if isGoodString([array objectAtIndex:index]) {
      return [array objectAtIndex:index];
    }
  }
  return @"";
}