summaryrefslogtreecommitdiff
path: root/euler74.c
blob: a0020f6b450a1606e92359a3c02a2aa77651ac9d (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
#include <stdio.h>
#include <string.h>

#define MAXTERM 3000000
int next[MAXTERM];

const int factorial[10] = {1, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880};

int sum_fact_digits(int n)
{
	int sum = 0;
	while (n > 0) {
		sum += factorial[n%10];
		n /= 10;
	}
	return sum;
}

void init()
{
	memset(next, 0, sizeof(next));
	for (int i = 1; i < 1000000; i++) {
		if (next[i])
			continue;
		next[i] = sum_fact_digits(i);
		for (int j = next[i]; next[j] == 0; j = next[j]) {
			next[j] = sum_fact_digits(j);
		}
	}
}

int chainlen(int n)
{
	int chain[100], L = 0;

	while (1) {
		for (int i = 0; i < L; i++) {
			if (chain[i] == n)
				return L;
		}
		chain[L] = n;
		L++;
		n = next[n];
	}
}

int main()
{
	int count = 0;

	init();
	for (int i = 1; i <= 1000000; i++) {
		if (chainlen(i) == 60)
			count++;
	}
	printf("%d\n", count);
}