This code in Java is a Knuth shuffle implementation, but a deterministic, seed-driven random number generator.
public String shuffleString(String data, long shuffleSeed) {
if(shuffleSeed!=0) {
Random rnd = new Random(shuffleSeed);
StringBuilder sb = new StringBuilder(data);
int n = data.length();
while(n>1) {
int k = rnd.nextInt(n--);
char t = sb.charAt(n);
sb.setCharAt(n, sb.charAt(k));
sb.setCharAt(k, t);
}
return sb.toString();
}
else {
return data;
}
}
How can I implement deterministic shuffling in Objective-C that outputs the same shuffle order with the same seed? I am using srandom (_shuffleSeed); and random ()% (n--), knowing that arc4_random is better, but cannot be seeded.
- (NSString*) shuffleString:(NSString*) data withShuffleSeed:(int) shuffleSeed {
if(shuffleSeed!=0) {
srandom(_shuffleSeed);
NSMutableString *result = [[NSMutableString alloc] initWithString:data];
unsigned long n = data.length;
while(n>1) {
unsigned long k = random()%(n--);
unichar t = [result characterAtIndex:n];
NSRange r1 = {n,1};
[result replaceCharactersInRange:r1 withString:[NSString stringWithFormat:@"%c", [result characterAtIndex:k]]];
NSRange r2 = {k,1};
[result replaceCharactersInRange:r2 withString:[NSString stringWithFormat:@"%c", t]];
}
return result;
}
else {
return data;
}
}
Currently, two shuffling methods do not generate the same result for the same input parameters. I'm sure something is missing from me!
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