156 lines
4.1 KiB
Objective-C
156 lines
4.1 KiB
Objective-C
#import <Foundation/Foundation.h>
|
|
|
|
|
|
@interface HuffmanTree : NSObject {
|
|
int freq;
|
|
}
|
|
-(id)initWithFreq:(int)f;
|
|
@property (readonly) int freq;
|
|
@end
|
|
|
|
@implementation HuffmanTree
|
|
@synthesize freq; // the frequency of this tree
|
|
-(id)initWithFreq:(int)f {
|
|
if (self = [super init]) {
|
|
freq = f;
|
|
}
|
|
return self;
|
|
}
|
|
@end
|
|
|
|
|
|
const void *HuffmanRetain(CFAllocatorRef allocator, const void *ptr) {
|
|
return [(id)ptr retain];
|
|
}
|
|
void HuffmanRelease(CFAllocatorRef allocator, const void *ptr) {
|
|
[(id)ptr release];
|
|
}
|
|
CFComparisonResult HuffmanCompare(const void *ptr1, const void *ptr2, void *unused) {
|
|
int f1 = ((HuffmanTree *)ptr1).freq;
|
|
int f2 = ((HuffmanTree *)ptr2).freq;
|
|
if (f1 == f2)
|
|
return kCFCompareEqualTo;
|
|
else if (f1 > f2)
|
|
return kCFCompareGreaterThan;
|
|
else
|
|
return kCFCompareLessThan;
|
|
}
|
|
|
|
|
|
@interface HuffmanLeaf : HuffmanTree {
|
|
char value; // the character this leaf represents
|
|
}
|
|
@property (readonly) char value;
|
|
-(id)initWithFreq:(int)f character:(char)c;
|
|
@end
|
|
|
|
@implementation HuffmanLeaf
|
|
@synthesize value;
|
|
-(id)initWithFreq:(int)f character:(char)c {
|
|
if (self = [super initWithFreq:f]) {
|
|
value = c;
|
|
}
|
|
return self;
|
|
}
|
|
@end
|
|
|
|
|
|
@interface HuffmanNode : HuffmanTree {
|
|
HuffmanTree *left, *right; // subtrees
|
|
}
|
|
@property (readonly) HuffmanTree *left, *right;
|
|
-(id)initWithLeft:(HuffmanTree *)l right:(HuffmanTree *)r;
|
|
@end
|
|
|
|
@implementation HuffmanNode
|
|
@synthesize left, right;
|
|
-(id)initWithLeft:(HuffmanTree *)l right:(HuffmanTree *)r {
|
|
if (self = [super initWithFreq:l.freq+r.freq]) {
|
|
left = [l retain];
|
|
right = [r retain];
|
|
}
|
|
return self;
|
|
}
|
|
-(void)dealloc {
|
|
[left release];
|
|
[right release];
|
|
[super dealloc];
|
|
}
|
|
@end
|
|
|
|
|
|
HuffmanTree *buildTree(NSCountedSet *chars) {
|
|
|
|
CFBinaryHeapCallBacks callBacks = {0, HuffmanRetain, HuffmanRelease, NULL, HuffmanCompare};
|
|
CFBinaryHeapRef trees = CFBinaryHeapCreate(NULL, 0, &callBacks, NULL);
|
|
|
|
// initially, we have a forest of leaves
|
|
// one for each non-empty character
|
|
for (NSNumber *ch in chars) {
|
|
int freq = [chars countForObject:ch];
|
|
if (freq > 0)
|
|
CFBinaryHeapAddValue(trees, [[[HuffmanLeaf alloc] initWithFreq:freq character:(char)[ch intValue]] autorelease]);
|
|
}
|
|
|
|
NSCAssert(CFBinaryHeapGetCount(trees) > 0, @"String must have at least one character");
|
|
// loop until there is only one tree left
|
|
while (CFBinaryHeapGetCount(trees) > 1) {
|
|
// two trees with least frequency
|
|
HuffmanTree *a = (HuffmanTree *)CFBinaryHeapGetMinimum(trees);
|
|
CFBinaryHeapRemoveMinimumValue(trees);
|
|
HuffmanTree *b = (HuffmanTree *)CFBinaryHeapGetMinimum(trees);
|
|
CFBinaryHeapRemoveMinimumValue(trees);
|
|
|
|
// put into new node and re-insert into queue
|
|
CFBinaryHeapAddValue(trees, [[[HuffmanNode alloc] initWithLeft:a right:b] autorelease]);
|
|
}
|
|
HuffmanTree *result = [(HuffmanTree *)CFBinaryHeapGetMinimum(trees) retain];
|
|
CFRelease(trees);
|
|
return [result autorelease];
|
|
}
|
|
|
|
void printCodes(HuffmanTree *tree, NSMutableString *prefix) {
|
|
NSCAssert(tree != nil, @"tree must not be nil");
|
|
if ([tree isKindOfClass:[HuffmanLeaf class]]) {
|
|
HuffmanLeaf *leaf = (HuffmanLeaf *)tree;
|
|
|
|
// print out character, frequency, and code for this leaf (which is just the prefix)
|
|
NSLog(@"%c\t%d\t%@", leaf.value, leaf.freq, prefix);
|
|
|
|
} else if ([tree isKindOfClass:[HuffmanNode class]]) {
|
|
HuffmanNode *node = (HuffmanNode *)tree;
|
|
|
|
// traverse left
|
|
[prefix appendString:@"0"];
|
|
printCodes(node.left, prefix);
|
|
[prefix deleteCharactersInRange:NSMakeRange([prefix length]-1, 1)];
|
|
|
|
// traverse right
|
|
[prefix appendString:@"1"];
|
|
printCodes(node.right, prefix);
|
|
[prefix deleteCharactersInRange:NSMakeRange([prefix length]-1, 1)];
|
|
}
|
|
}
|
|
|
|
int main(int argc, const char * argv[]) {
|
|
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
|
|
|
|
NSString *test = @"this is an example for huffman encoding";
|
|
|
|
// read each character and record the frequencies
|
|
NSCountedSet *chars = [[NSCountedSet alloc] init];
|
|
int n = [test length];
|
|
for (int i = 0; i < n; i++)
|
|
[chars addObject:[NSNumber numberWithInt:[test characterAtIndex:i]]];
|
|
|
|
// build tree
|
|
HuffmanTree *tree = buildTree(chars);
|
|
[chars release];
|
|
|
|
// print out results
|
|
NSLog(@"SYMBOL\tWEIGHT\tHUFFMAN CODE");
|
|
printCodes(tree, [NSMutableString string]);
|
|
|
|
[pool drain];
|
|
return 0;
|
|
}
|