``哈夫曼树是二叉树的一种特别应用,哈夫曼树仍然是一颗二叉树,只是其满足一定条件(带权最短路径二叉树)

1-求字符串中字母出现概率

这里先尝试实现取出一个由英文字母组成的字符串中每个出现的字母及其出现的次数
需求分析:1,从键盘输入一个字符串
2,对该字符串中出现的字符进行频度统计
3,根据频度统计,完成哈夫曼树
4,根据哈夫曼树得到每一个字符的哈夫曼编码
5,将原字符串中的每一个字符,与其相对应的哈夫曼编码代替,得到结果
6,将结果还原成原字符串

这里先实现最简单的求字符串中每个字符的频度

这样就完成了对字符串中字符的出现频率分析,再加上显示函数就完成了这个功能

2-初始化并创建一棵哈夫曼树

3-进行初步的哈夫曼编码

当完成了取得一个字符串中各个字符的频度和生成其对应的哈夫曼树后,接下来进行编码,即对每一个字符转化成其对应的哈夫曼编码,得到一个由1和0组成的字符串,这里的1和0先用一个字节代替,这也是一种加密的方法

由于增添了新的内容,初始化哈夫曼表和显示哈夫曼表的内容也需要更改

改动过的showhufftree增添一个新的打印值,即code

接下来要显示编码的结果,将字符串转化成一个由1 0组成的字符串,每个字符对应若干个1 0

在增加销毁的函数

4-初步的哈夫曼解码

这样就完成了对一个字符串的编码与解码
#include <stdio.h> #include <malloc.h> #include <string.h> #include "mec.h" #
include "huffman.h" FREQ *getFreq(const char *str, int *count); FREQ *getFreq(
const char *str, int *count) { FREQ *result = NULL; int alpha[256] = {0}; int
index; int alphaCount = 0; int i = 0; for(index = 0; str[index]; index++) { ++
alpha[str[index]]; } for(index = 0; index < 256; index++) { if(alpha[index] > 0)
{ alphaCount++; } } *count = alphaCount; result = (FREQ *)calloc(sizeof(FREQ),
alphaCount); for(index = 0; index < 256; index++) { if(alpha[index] > 0) {
result[i].ch = index; result[i++].freq = alpha[index]; } } return result; } void
showFreq(const FREQ *freq, int count); void showFreq(const FREQ *freq, int count
) { int i; printf("字符及其频度如下\n"); for(i = 0; i < count; i++) { printf("%c %d\n",
freq[i].ch, freq[i].freq); } } HUFFMAN *initHuffmanTable(const FREQ *freq, const
int count, int *hufIndex); HUFFMAN *initHuffmanTable(const FREQ *freq, const int
count, int *hufIndex) { HUFFMAN *hufTab = NULL; int index; hufTab = (HUFFMAN *)
calloc(sizeof(HUFFMAN), 2*count - 1); for(index = 0; index < count; index++) {
hufTab[index].freq = freq[index]; hufTab[index].left = freq[index].right = -1;
hufTab[index].visited = FALSE; hufTab[index].code = (char *)calloc(sizeof(char),
count); hufIndex[freq[index].ch] = index; } return hufTab; } void showHuffTree(
const HUFFMAN *huf, const int count); void showHuffTree(const HUFFMAN *huf,
const int count) { int i; int ch; printf("%-5s%-5c%-5d%-7d%-7d%-5s%s\n", "下标",
"字符", "频度", "左孩子", "右孩子", "访问", "编码"); for (i = 0; i < 2*count - 1; i++) { ch =
huf[i].freq.ch; printf("%-5d%-5c%-5d%-7d%-7d%-5s%s\n", i, ch == 0 ? '#' : ch,
huf[i].freq.freq, huf[i].left, huf[i].right, huf[i].visited ? "√" :"×", huf[i].
code== NULL ? "无" : huf[i].code); } void findMIn(HUFFMAN *huf, int count); void
findMin(HUFFMAN *huf, int count) { int minIndex = -1; int index; for(index = 0;
index< count; index ++) { if(FALSE == huf[index].visited && (minIndex == -1 ||
huf[index].freq.freq < huf[minIndex].freq.freq)) { minIndex = index; } } huf[
minIndex].visited = TRUE; return minIndex; } void makeHuffmanTable(HUFFMAN *huf,
int count); void makeHuffmanTable(HUFFMAN *huf, int count) { int left; int right
; int i; for(i = 0; i < count - 1; i++) { left = findMin(huf, count + i); right
= findMin(huf, count + i); huf[count + i].freq.ch = '#'; huf[count + i].freq.
freq= huf[left].freq.freq +huf[right].freq.freq; huf[count + i].left = left; huf
[count + i].right = right; huf[count + i].visited = FALSE } } void
destoryHuffmanTable(HUFFMAN *huf, int count); void destoryHuffmanTable(HUFFMAN *
huf, int count) { int i; for(i = 0; i < count; i++) { free(huf[i].code); } free(
huf); } void makeHuffmanCode(HUFFMAN *huf, int root, char *code, int index);
void makeHuffmanCode(HUFFMAN *huf, int root, char *code, int index) { if(-1 ==
huf[root].left) { code[index] = 0; strcpy(huf[root].root, code); return; } code[
index] = '0'; makeHuffmanCode(huf, huf[root].left, code, index+1); code[index] =
'1'; makeHuffmanCode(huf, huf[root].right, code, index+1); } int getBitsCount(
HUFFMAN*huf, int count) { int cnt; int i; for(i = 0; i < count; i++) { cnt +=
strlen(huf[i].code) * huf[i].freq.freq; } return cnt; } char *codding(const char
*str, HUFFMAN *huf, int count, int *hufIndex) { int index; int i; char *result =
NULL; result = (char *)calloc(sizeof(char), getBitsCount(huf, count) + 1);
printf("对字符串[%s]编码结果为:n", str); for(index = 0; str[index]; index++) { strcat(
result, huf[hufIndex[str[index]]].code); } return result; } void encodding(const
char *code, HUFFMAN *huf, int count) { int index = 0; int root = 2 * (count - 1)
; int bitCount; printf("解码结果为:\n"); bitCount = getBitsCount(huf, count); while(
index<= bitCount) { if(-1 == huf[root].left) { printf("%c", huf[root].freq.ch);
root= 2 * (count - 1) { break; } continue; } root = '1' == code[index] ? huf[
root].right : huf[root].left; index++; } printf("\n"); } int main(int argc, char
const *argv[]) { FREQ *freq = NULL; HUFFMAN *hufTab = NULL; char str[80]; int
alphaCount; char code[256] = {0}; int hufIndex[256] = {0}; char *res; printf(
"请输入一个字符串\n"); gets(str); freq = getFreq(str, &alphaCount); showFreq(freq,
alphaCount); hufTab = initHuffmanTable(freq, alphaCount, hufIndex);
makeHuffmanTable(hufTab, alphaCount); makeHuffmanCode(hufTab, 2*(alphaCount - 1)
, code, 0); showHuffTree(hufTab, alphaCount); res = codding(str, hufTab,
alphaCount, hufIndex); printf("字符串[%s]的编码结果为:\n %s\n", str, res); encodding(res,
hufTab, alphaCount); free(freq); destoryHuffmanTable(hufTab, alphaCount); free(
res); return 0; }

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