forked from nayuki/Project-Euler-solutions
-
Notifications
You must be signed in to change notification settings - Fork 0
Expand file tree
/
Copy pathp051.java
More file actions
84 lines (67 loc) · 1.86 KB
/
p051.java
File metadata and controls
84 lines (67 loc) · 1.86 KB
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
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
/*
* Solution to Project Euler problem 51
* Copyright (c) Project Nayuki. All rights reserved.
*
* https://www.nayuki.io/page/project-euler-solutions
* https://github.com/nayuki/Project-Euler-solutions
*/
import java.util.Arrays;
public final class p051 implements EulerSolution {
public static void main(String[] args) {
System.out.println(new p051().run());
}
public String run() {
boolean[] isPrime = Library.listPrimality(1000000);
for (int i = 0; i < isPrime.length; i++) {
if (!isPrime[i])
continue;
int[] n = toDigits(i);
for (int mask = 0; mask < (1 << n.length); mask++) {
int[] digits = doMask(n, mask);
int count = 0;
for (int j = 0; j < 10; j++) {
if (digits[0] != 0 && isPrime[toNumber(digits)])
count++;
digits = addMask(digits, mask);
}
if (count == 8) {
digits = doMask(n, mask);
for (int j = 0; j < 10; j++) {
if (digits[0] != 0 && isPrime[toNumber(digits)])
return Integer.toString(toNumber(digits));
digits = addMask(digits, mask);
}
}
}
}
throw new RuntimeException("Not found");
}
private static int[] toDigits(int n) {
int[] buf = new int[10];
int i = buf.length;
do {
i--;
buf[i] = n % 10;
n /= 10;
} while (n != 0);
return Arrays.copyOfRange(buf, i, buf.length);
}
private static int[] doMask(int[] digits, int mask) {
int[] result = new int[digits.length];
for (int i = 0; i < digits.length; i++)
result[i] = digits[i] * (~mask >>> i & 1);
return result;
}
private static int[] addMask(int[] digits, int mask) {
int[] result = new int[digits.length];
for (int i = 0; i < digits.length; i++)
result[i] = digits[i] + (mask >>> i & 1);
return result;
}
private static int toNumber(int[] digits) {
int result = 0;
for (int x : digits)
result = result * 10 + x;
return result;
}
}