POJ 1007 DNA Sorting

# include <stdio.h>

typedef struct {
char s[51];
int w, id;
}DNA;

int m, n;
DNA a[101];

int DNA_cmp(const void *x, const void *y)
{
int tmp = (*(DNA*)x).w - (*(DNA*)y).w;
if (tmp < 0) return -1;
if ((tmp == 0 && (*(DNA*)x).id < (*(DNA*)y).id)) return -1;
return 1;
}

int compute(char *s)
{
int i, j, ret;

ret = 0;
for ( i = 0; i < n; ++i)
{
for ( j = i + 1; j < n; ++j)
if (s[i] > s[j]) ++ret;
}
return ret;
}

int main()
{
int i, j;

while (~scanf("%d%d", &n, &m))
{
for ( i = 1; i <= m; ++i)
{
a[i].id = i;
scanf("%s", a[i].s);
a[i].w = compute(a[i].s);
}

qsort(a+1, m, sizeof(DNA), DNA_cmp);

for ( i = 1; i <= m; ++i)
puts(a[i].s);
}

return 0;
}