Huffman coding.

/* Huffman coding is widely used in video audio and image compression. * It can greatly reduce the size of files. The following codes show the * basic principle of huffman coding. * by: double; version:0.1;date:2009-08-01 */#include "/usr/c/head.h"#define INT_MAX ((int)(~0U >> 1))#define MAX 100typedef struct huffman_tree_node {unsigned int weight;unsigned int parent, lchild, rchild;}huffman_tree_node, *huffman_tree;typedef char ** huffman_code;status get_child(huffman_tree p, int n, int *c1, int *c2) {int i, temp, m, min;m = 0;min = INT_MAX;for (i = 1; i < n; ++i)if (p[i].parent == 0 && min > p[i].weight) { /* Here, "p" is a pointer variable, inertia made me write "min > p->weight" at some time in the past. * So, I should open my eyes. */ m = i;min = p[i].weight;}*c1 = m;m = 0;min = INT_MAX;for (i = 1; i < n; ++i)if (p[i].parent == 0 && min > p[i].weight && i != *c1) {m = i;min = p[i].weight;}*c2 = m;if (*c1 > *c2) {temp = *c1;*c1 = *c2;*c2 = temp;}return OK;}status huffman_coding(huffman_tree *HT, huffman_code *HC, int *w, int n) {int i, m, c1, c2, start, c, f;huffman_tree p;char * cd;m = 2 * n - 1;*HT = (huffman_tree)malloc(sizeof(huffman_tree_node) * (m + 1));if (!(*HT)) exit(OVERFLOW);/* There is close contact between the following "for" statement. * once, I wrote the first for loops like this: "for (i = 0, p = *HT + 1; i < n; ++i, ++p, ++w)". * and the second for loops keep the same like the following. Gcc (version 4.0 in FC4) worked normally * when compiling. But when I executed, FC4 reported a segmentation fault.It is strange that, * in Visual C++ 6.0 and FC10 no faults are reported even if there is indeed a cross-border error. */for (i = 1, p = *HT + 1; i <= n; ++i, ++p, ++w) {p->weight = *w;p->parent = p->lchild = p->rchild = 0;}for (; i <= m; ++i, ++p)p->weight = p->parent = p->lchild = p->rchild = 0;for (i = n + 1; i <= m; ++i) {get_child(*HT, i, &c1, &c2);(*HT)[i].lchild = c1;(*HT)[i].rchild = c2;(*HT)[i].weight = (*HT)[c1].weight + (*HT)[c2].weight;(*HT)[c1].parent = (*HT)[c2].parent = i;}*HC = (huffman_code)malloc(sizeof(char *) * (n + 1));if (!(*HC)) exit(OVERFLOW);cd = (char *)malloc(sizeof(char) * n);if (!cd) exit(OVERFLOW);cd[n - 1] = '/0';for (i = 1; i <= n; ++i) {start = n - 1 ;for (c = i, f = (*HT)[i].parent; f != 0; c = f, f = (*HT)[f].parent) {if ((*HT)[f].lchild == c)cd[--start] = '0';else cd[--start] = '1';}(*HC)[i] = (char *)malloc(sizeof(char) * (n - start));if (!(*HC)[i]) exit(OVERFLOW);strcpy((*HC)[i], cd + start);}free(cd);/* After malloc , a clear free is needed.*/return OK;}status print_code(huffman_code HC, int n) {int i;for (i = 1; i <= n; ++i) printf("%s/n", HC[i]);return OK;}int main(void) {huffman_tree HT;huffman_code HC;int temp, n, weight[MAX], i;printf("How many:");SCAN_INT(n, temp);if (n <= 1 || n > MAX - 1) {printf("No need or input error!/n");exit(ERROR);}for (i = 1; i <= n; ++i) {printf("No.%d:", i);SCAN_INT(weight[i], temp);}huffman_coding(&HT, &HC, weight + 1, n);printf("The huffman code are:/n");print_code(HC, n);return 0;}