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Ingy döt Net 2013-10-27 22:24:23 +00:00
parent 6f050a029e
commit 776bba907c
3887 changed files with 59894 additions and 7280 deletions
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30
Task/N-queens-problem/D/n-queens-problem-2.d
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@ -1,6 +1,6 @@
import std.stdio, std.conv;
uint nQueens(in uint nn) pure nothrow
ulong nQueens(in uint nn) pure nothrow
in {
assert(nn > 0 && nn <= 27,
"'side' value must be in 1 .. 27.");
@ -12,9 +12,9 @@ in {
immutable uint full = uint.max - ((1 << (ulen - nn)) - 1);
immutable n = nn - 3;
uint count;
typeof(return) count;
uint[32] l=void, r=void, c=void;
uint[33] mm; // mm and mmi are a stack
uint[33] mm; // mm and mmi are a stack.
// Require second queen to be left of the first queen, so
// we ever only test half of the possible solutions. This
@ -24,22 +24,22 @@ in {
uint d = n;
// c: columns occupied by previous queens.
c[n] = b0 | b1;
// l: columns attacked by left diagonals
// l: columns attacked by left diagonals.
l[n] = (b0 << 2) | (b1 << 1);
// r: by right diagnoals
// r: by right diagnoals.
r[n] = (b0 >> 2) | (b1 >> 1);
// availabe columns on current row
// Availabe columns on current row.
uint bits = full & ~(l[n] | r[n] | c[n]);
uint mmi = 1;
mm[mmi] = bits;
while (bits) {
// d: depth, aka row. counting backwards
// because !d is often faster than d != n
// d: depth, aka row. counting backwards.
// Because !d is often faster than d != n.
while (d) {
// pos is right most nonzero bit
// immutable uint pos = 1U << bits.bsf; // Slower.
immutable uint pos = -(cast(int)bits) & bits;
// Mark bit used. Only put current bits on
@ -53,9 +53,9 @@ in {
}
d--;
l[d] = (l[d+1] | pos) << 1;
r[d] = (r[d+1] | pos) >> 1;
c[d] = c[d+1] | pos;
l[d] = (l[d + 1] | pos) << 1;
r[d] = (r[d + 1] | pos) >> 1;
c[d] = c[d + 1] | pos;
bits = full & ~(l[d] | r[d] | c[d]);
@ -84,7 +84,7 @@ in {
return count * 2;
}
void main(string[] args) {
immutable int side = (args.length >= 2) ? to!int(args[1]) : 8;
writefln("N-queens(%d) = %d solutions.", side, nQueens(side));
void main(in string[] args) {
immutable uint side = (args.length >= 2) ? args[1].to!uint : 8;
writefln("N-queens(%d) = %d solutions.", side, side.nQueens);
}