NOJ数据结构实验007——哈夫曼编/译码器

冷不防 2023-01-18 04:21 117阅读 0赞

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本题简单思路：  
1.先建立一棵哈夫曼树，在建立时需要将叶结点对应的字符记录在树中。

2.我们需要建立一套译码系统，将叶结点中存储字符对应的译码存储到字符串数组hc中。建立时，我们需要从叶结点开始进行记录，即从下到上，我们将每次得到的译码先存储在字符串cd中（cd长度不会超过叶结点个数），并且时从cd最后（结束符\\0前）开始记录（因为之前是反的，负负得正），之后整合在hc中。

3.之后我们要在建立一套反译码系统。众所周知，哈夫曼编码是前缀编码，所以我们只需要将记录报文的字符串code与刚才字符串数组hc中每一项比较hc此项的长度len\_hc（用strncmp函数），直到找到将其strcat到字符串recode中，再将code向后推len\_hc位，直至比较完。

4.输出即可

#include<stdio.h>
    #include<stdlib.h>
    #include<string.h>
    
    #define N 30     //叶子结点最大值
    #define M 2*N-1  //所有结点最大值
    
    typedef struct
    {
        
    	int flag;
    	char data;
    	int weight;
    	int parent, LChild, RChild;
    }HTNode, HuffmanTree[M + 1]; //0号单元不用
    
    typedef char* HuffmanCode[N + 1];
    
    void InitHuffman(HuffmanTree ht, int w[], char str[], int n);
    //初始化哈夫曼树
    void CreateHuffman(HuffmanTree ht, int w[], int n);
    //构建哈夫曼树ht[M+1],w[]存放n个权值
    void Select(HuffmanTree ht, int tmp, int* s1, int* s2);
    //找到ht中权值最小的两个结点
    void CrtHuffmanCode(HuffmanTree ht, HuffmanCode hc, int n);
    //构建哈夫曼编码
    void GetCode(HuffmanTree ht, HuffmanCode hc, char* target, char* code, int n);
    //获得二进制编码
    void PrintCode(char* code);
    //打印编码
    void GetReCode(HuffmanTree ht, HuffmanCode hc, char* code, char *recode, int n);
    //二进制码重新编译成报文
    void PrintReCode(char* recode);
    //打印报文
    
    int main()
    {
        
    	int n; //n个权值
    	scanf("%d", &n);
    	char *str;
    	str = (char*)malloc(sizeof(char) * (n+1));
    	if (str == NULL) return 0;
    	for (int i = 1; i <= n; i++) {
        
    		getchar();
    		scanf("%c", &str[i]);
    	}
    	int *w;
    	w = (int*)malloc(sizeof(int) * (n+1));
    	if (w == NULL) return 0;
    	for (int i = 1; i <= n; i++) {
        
    		scanf("%d", &w[i]);
    	}
    	HuffmanTree ht;
    	InitHuffman(ht, w, str, n);
    	CreateHuffman(ht, w, n);
    	HuffmanCode hc;
    	CrtHuffmanCode(ht, hc, n);
    	char target[200], code[200];
    	scanf("%s", target);
    	GetCode(ht, hc, target, code, n);
    	PrintCode(code);
    	char recode[200];
        GetReCode(ht, hc, code, recode, n);
        PrintReCode(recode);
    	return 0;
    }
    
    void InitHuffman(HuffmanTree ht, int w[], char str[], int n)
    {
           //初始化哈夫曼树
    	ht[0].flag = 0;
    	for (int i = 1; i <= n; i++) {
        
    		//将前n项初始化
    		ht[i].flag = ht[i - 1].flag + 1;
    		ht[i].weight = w[i];
    		ht[i].parent = 0;
    		ht[i].LChild = 0;
    		ht[i].RChild = 0;
    		ht[i].data = str[i];
    	}
    	int m = 2 * n - 1;
    	for (int i = n + 1; i <= m; i++) {
        
    		//将n+1项到m项初始化
    		ht[i].flag = ht[i - 1].flag + 1;
    		ht[i].weight = 0;
    		ht[i].parent = 0;
    		ht[i].LChild = 0;
    		ht[i].RChild = 0;
    	}
    }
    
    void CreateHuffman(HuffmanTree ht, int w[], int n)
    {
           //构建哈夫曼树ht[M+1],w[]存放n个权值
    	int s1, s2;
    	int m = 2 * n - 1;
    	for (int i = n + 1; i <= m; i++) {
        
    		//开始构造
    		Select(ht, i-1, &s1, &s2);
    		ht[i].weight = ht[s1].weight + ht[s2].weight;
    		if (ht[s1].weight < ht[s2].weight) {
        
                ht[i].LChild = s1;
                ht[i].RChild = s2;
    		}
    		else {
        
                ht[i].LChild = s2;
                ht[i].RChild = s1;
    		}
    		ht[s1].parent = i;
    		ht[s2].parent = i;
    	}
    }
    
    void Select(HuffmanTree ht, int n, int* s1, int* s2)
    {
           //找到ht中权值最小的两个结点
    	int min = 0, tmp;
    	for (int i = 1; i <= n; i++) {
        
    		if (ht[i].parent == 0) {
        
    			min = i;
    			tmp = ht[i].weight;
    			break;
    		}
    	}
    	for (int i = 1; i <= n; i++) {
        
    		if (ht[i].parent == 0 && ht[i].weight < tmp) {
        
    			min = i;
    			tmp = ht[i].weight;
    		}
    	}
    	*s1 = min;
    	ht[min].parent = -1;
    	for (int i = 1; i <= n; i++) {
        
    		if (ht[i].parent == 0) {
        
    			min = i;
    			tmp = ht[i].weight;
    			break;
    		}
    	}
    	for (int i = 1; i <= n; i++) {
        
    		if (ht[i].parent == 0 && ht[i].weight < tmp) {
        
    			min = i;
    			tmp = ht[i].weight;
    		}
    	}
    	*s2 = min;
    }
    
    void CrtHuffmanCode(HuffmanTree ht, HuffmanCode hc, int n)
    {
           //构建哈夫曼编码
    	char* cd;
    	cd = (char*)malloc(sizeof(char) * n);//编码长度不超过n
    	if (cd == NULL) return;
    	cd[n - 1] = '\0';
    	for (int i = 1; i <= n; i++) {
        
    		int start = n - 1;//记录编码开始位置
    		int tmp = i, par = ht[i].parent;
    		while (par) {
        
    			start--;
    			if (ht[par].LChild == tmp) {
        
    				cd[start] = '0';
    			}
    			else {
        
    				cd[start] = '1';
    			}
    			tmp = par;
    			par = ht[par].parent;
    		}
    		hc[i] = (char*)malloc(sizeof(char) * (n - start));
    		if (hc[i] == NULL) return;
    		strcpy(hc[i], &cd[start]);
    	}
    	free(cd);
    }
    
    void GetCode(HuffmanTree ht, HuffmanCode hc, char* target, char* code, int n)
    {
           //获得二进制编码
    	int len = strlen(target);
    	code[0] = '\0';
    	for (int i = 0; i < len; i++) {
        
    		for (int j = 1; j <= n; j++) {
        
    			if (target[i] == ht[j].data) {
        
    				strcat(code, hc[j]);
    			}
    		}
    	}
    
    }
    
    void PrintCode(char* code)
    {
           //打印编码
    	printf("%s\n",code);
    }
    
    void GetReCode(HuffmanTree ht, HuffmanCode hc, char* code, char *recode, int n)
    {
           //二进制码重新编译成报文
    	int len_code = strlen(code);
    	int i= 0, k = 0;
    	while (i < len_code) {
        
    		for (int j = 1; j <= n; j++) {
        
    			if (code[i] == hc[j][0]) {
        
    				int len_hc = strlen(hc[j]);
    				if (strncmp(hc[j], &code[i], len_hc) == 0) {
        
    					recode[k] = ht[j].data;
    					k++;
    					i = i + len_hc;
    				}
    			}
    		}
    	}
    }
    
    void PrintReCode(char* recode)
    {
           //打印报文
        printf("%s\n",recode);
    }

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