来自 Cormen 的霍夫曼算法

Question

I'm trying to write a Huffman coding tree , by using multimap<int, NODE*> where NODE is just a classical tree node. So I have written this method:

this->CreateMapTree();
int n = (int)tree.size();
pair<int, NODE*> x, y, z;

for (int i = 0; i < n-1; ++i)
{
    x = *tree.begin(); tree.erase(tree.begin());
    y = *tree.begin(); tree.erase(tree.begin());

    z.second = new NODE;

    z.second->left = y.second;
    z.second->right = x.second;
    z.first = x.first + y.first;

    tree.insert(z);
}//after loop there is only one element in the tree


head = tree.begin()->second;

Method CreateMapTree work perfect, as the result I have tree . I used classical algorithm of сreating Huffman tree (from Cormen). I was checking this code many times, but I couldn't find my mistake. Code three is wrong and I can't create correct dictionary for encode and decode.

What is wrong?

Answer 1

I suggest you look at what happens to x and y after you delete them from the tree. Pointers to them may no longer be valid.