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#include <stdio.h>
#include <stdbool.h>
#include <math.h>
int lenHelper(int x)
{
if (x >= 10000000) return 8;
if (x >= 1000000) return 7;
if (x >= 100000) return 6;
if (x >= 10000) return 5;
if (x >= 1000) return 4;
if (x >= 100) return 3;
if (x >= 10) return 2;
return 1;
}
int get_digit(int nb, int digit_index)
{
if (digit_index == 1)
return nb % 10;
return (int)(nb / pow(10.0, (double)(digit_index-1))) % 10;
}
int next_iteration(int nb)
{
int i, sum = 0;
for (i = 0; i < lenHelper(nb); i++) {
sum += pow(get_digit(nb, i), 2);
}
return sum;
}
bool end_of_square_digit_chain_is_89(int nb)
{
bool once = false;
int next_nb;
for (int i = 0; i < 10; i++) {
// printf("%d", next_nb);
next_nb = next_iteration(nb);
if (next_nb == 89 || next_nb == 1) {
if (once) {
return next_nb == 89 ? true : false;
}
once = true;
}
nb = next_nb;
}
return false;
}
int main(void)
{
int i, counter = 0;
for (i = 1; i < 10000000; i++) {
// printf("%d\n", i);
if (end_of_square_digit_chain_is_89(i))
counter++;
if (i % 1000000 == 0)
printf("%d\n", counter);
}
printf("%d\n", counter);
return 0;
}
// def end_of_square_digit_chain_is_89(nb):
// once = False
// while True:
// next_nb = sum([int(x)**2 for x in str(nb)])
// if next_nb == 89 or next_nb == 1:
// if once:
// return True if next_nb == 89 else False
// once = True
// nb = next_nb
// counter = 0
// for i in range(1, 10_000_000):
// if end_of_square_digit_chain_is_89(i):
// counter += 1
// if i % 1000_000 == 0:
// print(counter)
// pass
// print(counter)
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