1.1 --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
     1.2 +++ b/src/collatz.c	Tue Oct 18 01:17:49 2011 -0700
     1.3 @@ -0,0 +1,40 @@
     1.4 +
     1.5 +#include <stdio.h>
     1.6 +#include <stdlib.h>
     1.7 +
     1.8 +int main(int argc, char *argv[]){
     1.9 +  FILE *fp;
    1.10 +  int n;
    1.11 +  if((fp=fopen(argv[1] ,"r")) == NULL) {
    1.12 +    printf("Cannot open file.\n");
    1.13 +    exit(1);}
    1.14 +  fscanf(fp, "%d", &n); /* read from file */
    1.15 +  int answer = search_collatz(n);
    1.16 +  printf("%d\n", answer); }
    1.17 +
    1.18 +long long collatz_next(long long n){
    1.19 +  if (!(n % 2)){
    1.20 +    return n/2;}
    1.21 +  else {
    1.22 +    return 1+(n*3);}}
    1.23 +
    1.24 +int collatz_length(int n){
    1.25 +  long long t = n;
    1.26 +  int d = 1;
    1.27 +  while (t > 1){
    1.28 +    t = collatz_next(t);
    1.29 +    d++;}
    1.30 +  return d;}
    1.31 +  
    1.32 +int search_collatz(int n){
    1.33 +  int max = 0;
    1.34 +  int max_val = 0;
    1.35 +  int temp_val;
    1.36 +  int i;
    1.37 +  for (i = 1; i<n; i++){
    1.38 +    temp_val = collatz_length(i);
    1.39 +    if (temp_val > max_val){
    1.40 +      max = i;
    1.41 +      max_val = temp_val;}}
    1.42 +  return max;}
    1.43 +