Iterated digits squaring: Difference between revisions
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This problem derives from the [https://projecteuler.net/problem=92 Project Euler problem 92].
=={{header|D}}==
This is a fast imperative brute-force solution.
<lang d>void main() nothrow @nogc {
import core.stdc.stdio: printf;
enum uint magic = 89;
enum uint limit = 100_000_000;
uint[(9 ^^ 2) * 8 + 1] lookup = void;
uint[10] squares;
foreach (immutable i, ref x; squares)
x = i ^^ 2;
foreach (immutable uint i; 1 .. lookup.length) {
uint x = i;
while (x != magic && x != 1) {
uint total = 0;
while (x) {
total += squares[(x % 10)];
x /= 10;
}
x = total;
}
lookup[i] = x == magic;
}
uint magicCount = 0;
foreach (immutable uint i; 1 .. limit) {
uint x = i;
uint total = 0;
while (x) {
total += squares[(x % 10)];
x /= 10;
}
magicCount += lookup[total];
}
printf("%u\n", magicCount);
}</lang>
{{out}}
<pre>85744333</pre>
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