langs a-z

Task/Knuths-algorithm-S/Objective-C/knuths-algorithm-s.m

@@ -0,0 +1,35 @@
+#import <Foundation/Foundation.h>
+
+typedef NSArray *(^SOfN)(id);
+
+SOfN s_of_n_creator(int n) {
+  NSMutableArray *sample = [NSMutableArray arrayWithCapacity:n];
+  __block int i = 0;
+  return [[^(id item) {
+    i++;
+    if (i <= n) {
+      [sample addObject:item];
+    } else if (rand() % i < n) {
+      [sample replaceObjectAtIndex:rand() % n withObject:item];
+    }
+    return sample;
+  } copy] autorelease];
+}
+
+int main(int argc, const char *argv[]) {
+  NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
+
+  NSCountedSet *bin = [[NSCountedSet alloc] init];
+  for (int trial = 0; trial < 100000; trial++) {
+    SOfN s_of_n = s_of_n_creator(3);
+    NSArray *sample;
+    for (int i = 0; i < 10; i++)
+      sample = s_of_n([NSNumber numberWithInt:i]);
+    [bin addObjectsFromArray:sample];
+  }
+  NSLog(@"%@", bin);
+  [bin release];
+
+  [pool release];
+  return 0;
+}