POJ_1521_Entropy_CE

最新推荐文章于 2020-04-21 22:18:58 发布

cxy7tv

最新推荐文章于 2020-04-21 22:18:58 发布

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CC 4.0 BY-SA版权

文章标签： huffman poj

本文链接：https://blog.youkuaiyun.com/cxy7tv/article/details/51049855

本文介绍了一种使用C++实现哈夫曼编码的方法。通过构建哈夫曼树并为每个字符分配唯一的二进制编码来压缩字符串数据。文章详细解释了如何选择权重最小的节点进行树的构建，并展示了如何遍历树以生成最终的哈夫曼编码。

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#include<iostream>
#include<sstream>
#include<string>
#include<vector>
#include<list>
#include<set>
#include<map>
#include<stack>
#include<queue>
#pragma warning(disable:4996)
using std::cin;
using std::cout;
using std::endl;
using std::stringstream;
using std::string;
using std::vector;
using std::list;
using std::pair;
using std::set;
using std::multiset;
using std::map;
using std::multimap;
using std::stack;
using std::queue;
using std::priority_queue;
class Node
{
private:
	char character;
	int weight;
	int parent, lchild, rchild;
	string code;
public:
	Node()
	{
		character = '\0';
		weight = parent = lchild = rchild = 0;
		code = "";
	}
	Node(const char &ch,const int &w)
	{
		character = ch;
		weight = w;
		parent = lchild = rchild = 0;
		code = "";
	}
	Node(const int &w,const int &first,const int &second)
	{
		character = '\0';
		weight = w;
		parent=0;
		lchild = std::min(first,second);
		rchild = std::max(first,second);
		code = "";
	}
	pair<int, int>select(const vector<Node>&HfTree)
	{
		pair<int, int>children;
		int max_first = INT_MAX, max_second = INT_MAX;
		for (size_t i = 1; i !=HfTree.size(); i++)
		{
			if (HfTree[i].weight < max_first&&!HfTree[i].parent)
			{
				max_second = max_first;
				children.second = children.first;
				max_first = HfTree[i].weight;
				children.first = i;
			}
			else if (HfTree[i].weight < max_second&&!HfTree[i].parent)
			{
				max_second = HfTree[i].weight;
				children.second = i;
			}
		}
		return children;
	}
	map<char, string> HfCoding(const map<char, int>&char_freq)
	{
		vector<Node>HfTree(1);
		for (auto iter = char_freq.begin();iter!=char_freq.end();iter++)
		{
			HfTree.push_back({ iter->first,iter->second });
		}
		for (size_t i = 0;i!=char_freq.size()-1;i++)
		{
			//找到两个权最少并且parent为0的结点
			pair<int, int>children = select(HfTree);
			HfTree[children.first].parent = HfTree.size();
			HfTree[children.second].parent = HfTree.size();
			HfTree.push_back({ HfTree[children.first] .weight+ HfTree[children.second].weight,children.first,children.second});
		}
		queue<int>Q;
		Q.push(HfTree.size() - 1);
		map<char, string>char_code;
		while (Q.size())
		{
			int i = Q.front(); 
			Q.pop();
			Node parent = HfTree[i];
			if (parent.character)
			{
				char_code[parent.character] = parent.code;
			}
			if (parent.lchild)
			{
				HfTree[parent.lchild].code = HfTree[i].code + '0';
				Q.push(parent.lchild);
			}
			if (parent.rchild)
			{
				HfTree[parent.rchild].code = HfTree[i].code + '1';
				Q.push(parent.rchild);
			}
		}
		return char_code;
	}
};

int main()
{
	//freopen("input.txt", "r", stdin);
	//freopen("output.txt", "w", stdout);
	string str;
	while (cin >> str)
	{
		if (str == "END")
		{
			break;
		}
		map<char, int>char_freq;
		for (size_t i = 0; i < str.size(); i++)
		{
			char_freq[str[i]]++;
		}
		if (char_freq.size() == 1)
		{
			cout << 8*str[0] << ' ' << 8*str[0] << ' ' << "1.0" << endl;
			continue;
		}
		Node HfTree;
		map<char,string>char_code=HfTree.HfCoding(char_freq);
		int length = 0;
		for (size_t i = 0; i < str.size(); i++)
		{
			length += char_code[str[i]].size();
		}
		cout << 8 * str.size() << ' ' << length << ' ';
		printf("%.1lf\n", 8.0*(double)str.size() / (double)length);
	}
	return 0;
}