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#include <stdio.h>
#include <string.h>
#include <ctype.h>
#include <stdlib.h>
/* The C Programming Language: 2nd Edition
*
* Exercise 6-4: Write a program that prints the distinct words in its input
* sorted into decreasing order of frequency of occurrence. Precede each word
* by its count.
*
* Notes: The approach I took builds a separate sorted tree instead of
* modifying the tree in-place, like a lot of sorting functions tend to do.
* This meant doubling the amount of RAM needed to solve the exercise. There
* is probably a more elegant way to do this -- even within Category-0
* standards -- but I couldn't seem to figure it out. I'm disappointed that
* freq_sort and addsorted couldn't seem to be combined.
*/
#define BUFSIZE 1000
#define MAXWORD 100
#define DEF_PRE_LEN 4
struct tnode {
char *word;
int count;
struct tnode *left;
struct tnode *right;
};
char buf[BUFSIZE];
int bufp = 0;
int minlen;
int getch(void);
void ungetch(int);
int getword(char *, int);
struct tnode *addtree(struct tnode *, char *);
struct tnode *freq_sort(struct tnode *, struct tnode *);
struct tnode *addsorted(struct tnode *, struct tnode *);
void treeprint(struct tnode *);
struct tnode *talloc(void);
char *mystrdup(char *);
int main(int argc, char *argv[]) {
switch (argc) {
case 1:
minlen = DEF_PRE_LEN;
break;
case 2:
minlen = strtol(argv[1], NULL, 10);
break;
default:
printf("Too many arguments.\n");
return 1;
}
struct tnode *root;
struct tnode *sorted;
char word[MAXWORD];
root = NULL;
sorted = NULL;
while (getword(word, MAXWORD) != EOF) {
/* Only add the words we need to the tree */
if (isalpha(word[0]) && strlen(word) > minlen) {
root = addtree(root, word);
}
}
/* Sort them in order of occurrence */
if (root == NULL) {
printf("No words at that length or greater were found.\n");
return 1;
} else {
sorted = freq_sort(root, sorted);
treeprint(sorted);
return 0;
}
}
/* Iterate over the "tree" and create a new, sorted tree */
struct tnode *freq_sort(struct tnode *p, struct tnode *s) {
for (; p != NULL; p = p->right) {
s = addsorted(p, s);
}
return s;
}
/* Add entries to the new tree, ordered by word frequency. I feel
* that this function and freq_sort() could somehow be consolidated
* and that this could be done better. Patches or PRs welcome.
*/
struct tnode *addsorted(struct tnode *p, struct tnode *s) {
if (s != NULL) {
if (p->count > s->count) {
s->left = addsorted(p, s->left);
} else {
s->right = addsorted(p, s->right);
}
} else {
s = talloc();
s->word = mystrdup(p->word);
s->count = p->count;
}
return s;
}
int getword(char *word, int lim) {
int c;
char *w = word;
while (isspace(c = getch())) {
}
if (c == EOF) {
return EOF;
}
if (c != EOF) {
*w++ = c;
}
for ( ; --lim > 0; w++) {
if (!isalpha(*w = getch())) {
ungetch(*w);
break;
}
}
*w = '\0';
return word[0];
}
int getch(void) {
return (bufp > 0) ? buf[--bufp] : getchar();
}
void ungetch(int c) {
if (bufp >= BUFSIZE) {
printf("ungetch: Too many characters.\n");
} else {
buf[bufp++] = c;
}
}
struct tnode *addtree(struct tnode *p, char *w) {
if (p != NULL) {
/* We're putting all new things to the right side to dumb our tree struct
* down to a list. It's technically one address larger than a linked list,
* but there's no harm in re-purposing a structure.
*/
if (strcasecmp(p->word, w) == 0) {
p->count++;
} else {
p->right = addtree(p->right, w);
}
} else {
p = talloc();
p->word = mystrdup(w);
p->count = 1;
}
return p;
}
void treeprint(struct tnode *p) {
if (p != NULL) {
treeprint(p->left);
printf("%4d %-20s\n", p->count, p->word);
treeprint(p->right);
}
}
struct tnode *talloc(void) {
return (struct tnode *) malloc(sizeof(struct tnode));
}
char *mystrdup(char *s) {
char *p;
p = (char *) malloc(strlen(s)+1);
if (p != NULL) {
strcpy(p , s);
}
return p;
}
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