Coding for Interviews: Reverse Words

reverse_words.c

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <assert.h>

#define SPACE ' '

void
reverse_words(char *sent, size_t len)
{
    size_t i;
    size_t start;
    size_t end;
    char tmp;

    /*
     * Reverse the entire string.
     */
    for (i = 0; i < len/2; ++i)
    {
        tmp = sent[i];
        sent[i] = sent[len-1-i];
        sent[len-1-i] = tmp;
    }

    /*
     * Find the first non-space element.
     */
    for (start = 0; start < end && sent[start] == SPACE; ++start)
        ;

    /*
     * Reverse individual words in the string.
     * Words are delimited by SPACE.
     */
    while (start < len)
    {
        for (end = start+1; end < len && sent[end] != SPACE; ++end)
            ;
        for (i = start; i < (start+end)/2; ++i)
        {
            tmp = sent[i];
            sent[i] = sent[end-1-i+start];
            sent[end-1-i+start] = tmp;
        }
        start = end+1;
    }
}

int
main(int argc, char **argv)
{
    char *sent = NULL;
    if (argc == 1)
    {
        char const *tmp = "Coding for Interviews contains too many gifs.";
        sent = (char *)malloc(sizeof(char)*strlen(tmp));
        assert(sent);
        strcpy(sent, tmp);
    }
    else
    {
        sent = (char *)malloc(sizeof(char)*strlen(argv[1]));
        assert(sent);
        strcpy(sent, argv[1]);
    }
    reverse_words(sent, strlen(sent));
    printf("`%s'\n", sent);
    free(sent);
}