// Calculate sample standard deviation using a histogram to see if
// that makes it faster.
// Answer: it doesn't.

#include <stdio.h>
#include <math.h>

int
main()
{
     int hist[256] = {0}, n = 0, sum = 0, sumsq = 0, c;
     
     while ((c = getchar()) != EOF) hist[(unsigned char)c]++;

     for (int ii = 0; ii < 256; ii++) {
          n += hist[ii];
          sum += ii * hist[ii];
          sumsq += ii * ii * hist[ii];
     }

     printf("Sample SD on %d bytes averaging %.3f is %.3f\n", 
            n,
            sum/(double)n,
            sqrt(sumsq - (double)sum*sum/n)/(n-1));
     return 0;
}