[mute@geek ~/test]$ ./n50 n50.txt
4

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

#define MAXLINES        32768

int lines[MAXLINES];
int line_count = 0;

int qsort_cmp(const void *p1, const void *p2)
{
        return (*(int *)p2 - *(int *)p1);
}

int main(int argc, char**argv)
{
        FILE *fh;
        char buf[512];
        int i, sum = 0, threshold;

        if (argc != 2)
        {
                printf("Usage: %s <input file>\n", argv[0]);
                return -1;
        }

        if ((fh = fopen(argv[1], "r")) == NULL)
        {
                perror("fopen");
                return -1;
        }

        while (fgets(buf, sizeof(buf), fh))
        {
                int len = strlen(buf);

                /* skip comments */
                if (buf[0] == '#') continue;

                /* strip newline at end */
                buf[--len] = 0;

                /* add to sum. */
                sum += len;

                /* keep record */
                lines[line_count++] = len;
        }

        qsort(lines, line_count, sizeof(int), qsort_cmp);

        threshold = sum / 2;

        for (i = sum = 0; (sum += lines[i]) < threshold; i++)
                ;

        printf("%d\n", lines[i]);

        return 0;
}