HuffForest* initForest(int* freq) { //根据频率统计表，为每个字符创建一棵树
HuffForest* forest = new HuffForest; //以List实现的Huffman森林
for (int i = 0; i < N_CHAR; i++) { //为每个字符
forest->insertAsLast(new HuffTree); //生成一棵树，并将字符及其频率
forest->last()->data->insertAsRoot(HuffChar(0x20+i, freq[i])); //存入其中
}
return forest;
}
HuffTree* generateTree ( HuffForest* forest ) { //Huffman编码算法
while ( 1 < forest->size() ) {
HuffTree* T1 = minHChar ( forest ); HuffTree* T2 = minHChar ( forest );
HuffTree* S = new HuffTree(); /*DSA*/printf ( "\n################\nMerging " ); print ( T1->root()->data ); printf ( " with " ); print ( T2->root()->data ); printf ( " ...\n" );
S->insertAsRoot ( HuffChar ( '^', T1->root()->data.weight + T2->root()->data.weight ) );
S->attachAsLC ( S->root(), T1 ); S->attachAsRC ( S->root(), T2 );
forest->insertAsLast ( S ); /*DSA*/ //print(forest);
} //assert: 循环结束时，森林中唯一（列表首节点中）的那棵树即Huffman编码树
return forest->first()->data;
}
/******************************************************************************************
* Huffman树构造算法：对传入的Huffman森林forest逐步合并，直到成为一棵树
******************************************************************************************
* forest基于优先级队列实现，此算法适用于符合PQ接口的任何实现方式
* 为Huffman_PQ_List、Huffman_PQ_ComplHeap和Huffman_PQ_LeftHeap共用
* 编译前对应工程只需设置相应标志：DSA_PQ_List、DSA_PQ_ComplHeap或DSA_PQ_LeftHeap
******************************************************************************************/
HuffTree* generateTree(HuffForest* forest) {
while (1 < forest->size()) {
HuffTree* s1 = forest->delMax(); HuffTree* s2 = forest->delMax();
HuffTree* s = new HuffTree();
/*DSA*/printf("Merging "); print(s1->root()->data); printf(" with "); print(s2->root()->data); printf(" ...\n");
s->insertAsRoot(HuffChar('^', s1->root()->data.weight + s2->root()->data.weight));
s->attachAsLC(s->root(), s1); s->attachAsRC(s->root(), s2);
forest->insert(s); //将合并后的Huffman树插回Huffman森林
}
HuffTree* tree = forest->delMax(); //至此，森林中的最后一棵树
return tree; //即全局Huffman编码树
}
