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Objective-C实现霍夫曼树
Huffman树（Huffman Tree）是一种用于数据压缩的二叉树结构，常用于构建霍夫曼编码。以下是用Objective-C语言实现霍夫曼树的详细示例和解释。
   
      #import 
    
       @interface HuffmanNode : NSObject  @property (nonatomic, assign) char character;  @end  @interface HuffmanTree : NSObject  @property (nonatomic, strong) HuffmanNode *root;  @property (nonatomic, strong) NSArray *nodes;  -(id)initWithCharacters:(NSArray *)characters;  -(HuffmanNode*)buildTree;  -(NSString*)huffmanCode:(char)char;  @end  @implementation HuffmanTree  -(id)initWithCharacters:(NSArray *)characters {    self = [super init];    self.nodes = [HuffmanNode nodesWithCharacters:characters];    return self;  }  -(HuffmanNode*)buildTree {    if ([self.nodes count] == 1) {      HuffmanNode *node = [self.nodes firstObject];      node.isLeaf = YES;      return node;    }    HuffmanNode *left = [self buildTreeForNodes:self.nodes range:0...([self.nodes count]/2)];    HuffmanNode *right = [self buildTreeForNodes:self.nodes range:([self.nodes count]/2)...[self.nodes count]];    if (left.character < right.character) {      left = [right swapWithLeft:left];    }    left.right = right;    right.left = left;    return left;  }  -(HuffmanNode*)buildTreeForNodes:(NSArray *)nodes range:(NSRange)range {    if (range.length == 1) {      HuffmanNode *node = [[HuffmanNode alloc] init];      node.character = [nodes[range.location]];      node.isLeaf = YES;      return node;    }    NSArray *subNodes = [nodes range:range];    HuffmanNode *left = [self buildTreeForNodes:subNodes range:0...([subNodes count]/2)];    HuffmanNode *right = [self buildTreeForNodes:subNodes range:([subNodes count]/2)...[subNodes count]];    if (left.character < right.character) {      left = [right swapWithLeft:left];    }    left.right = right;    right.left = left;    return left;  }  -(HuffmanNode*)swapWithLeft:(HuffmanNode*)left {    HuffmanNode *temp = left.right;    left.right = temp.right;    temp.right = left;    left = temp;    return left;  }  -(NSString*)huffmanCode:(char)char {    return [self buildTree].right.huffmanCode(char);  }  @end
    
   
Huffman树是一种基于频率的编码树，其核心思想是将最频繁出现的字符放在树的根部，递减到叶子节点。通过这种方式，高频字符可以使用较短的编码，而低频字符则需要更长的编码，从而实现压缩率的提升。

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