sys_prog/sortlines/sortlines.c

// vim: set ts=4 sw=4 et tw=80:
#include <stdio.h>
#include <ctype.h>
#include <unistd.h>
#include <string.h>
#include <stdbool.h>
#define MAX_LINE_SIZE 1001
#define DEBUG

void swap(char** a, char** b);
void print_words(char* words[], size_t start, size_t end);
void quicksort_string(char* strings[static 1], size_t start, size_t end);

void swap(char** a, char** b) {
    char* tmp;
    tmp = *a;
    *a = *b;
    *b = tmp;
}

void quicksort_string(char* strings[static 1], size_t start, size_t end) {

#ifdef DEBUG
    sleep(1);
    printf("%ld - %ld: ", start, end);
    print_words(strings, start, end);
    putchar('\n');
#endif

    if (end - start < 2) {
#ifdef DEBUG
        puts("returning");
#endif
        return;
    }

    char* pivot = strings[end - 1];
    size_t i, gt = end - 1;
    for (i = start; i < gt; i++) {
#ifdef DEBUG
        printf("i=%ld gt=%ld\n", i, gt);
        print_words(strings, start, end);
        putchar('\n');
#endif
        if (strcmp(strings[i], pivot) > 0) {
            swap(&strings[--gt], &strings[i--]);
        }
    }
    swap(&strings[gt], &strings[end - 1]);

#ifdef DEBUG
    print_words(strings, start, gt);
    printf("| %s | ", strings[gt]);
    print_words(strings, gt + 1, end);
    putchar('\n');
#endif

    quicksort_string(strings, start, gt);
    quicksort_string(strings, gt + 1, end);
}

void print_words(char* words[], size_t start, size_t end) {
    size_t i;
    for (i = start; i < end; i++) {
        printf("%s ", words[i] == NULL ? "NULL" : words[i]);
    }
}

int main() {
    char line[MAX_LINE_SIZE];
    char* words[MAX_LINE_SIZE / 2];
    char* word = line;
    size_t chars = 0, words_len = 0;
    int c;
    bool last_alpha = false;
    while ((c = getchar()) != EOF) {
        if (!isalpha(c) || c == '\n') {
            if (last_alpha) {
                line[chars++] = '\0';
                words[words_len++] = word;
                word = line + chars;
                last_alpha = false;
            }
            if (c == '\n') {
                quicksort_string(words, 0, words_len);
                print_words(words, 0, words_len);
                putchar('\n');
                chars = 0;
                words_len = 0;
                word = line;
            }
        } else {
            line[chars++] = c;
            last_alpha = true;
        }
    }
}