clang/test/SemaCXX/constexpr-nqueens.cpp

   1 // RUN: %clang_cc1 -std=c++11 -fsyntax-only %s
   2
   3 typedef unsigned long uint64_t;
   4
   5 struct Board {
   6   uint64_t State;
   7   bool Failed;
   8
   9   constexpr Board() : State(0), Failed(false) {}
  10   constexpr Board(const Board &O) : State(O.State), Failed(O.Failed) {}
  11   constexpr Board(uint64_t State, bool Failed = false) :
  12     State(State), Failed(Failed) {}
  13   constexpr Board addQueen(int Row, int Col) const {
  14     return Board(State | ((uint64_t)Row << (Col * 4)));
  15   }
  16   constexpr int getQueenRow(int Col) const {
  17     return (State >> (Col * 4)) & 0xf;
  18   }
  19   constexpr bool ok(int Row, int Col) const {
  20     return okRecurse(Row, Col, 0);
  21   }
  22   constexpr bool okRecurse(int Row, int Col, int CheckCol) const {
  23     return Col == CheckCol ? true :
  24            getQueenRow(CheckCol) == Row ? false :
  25            getQueenRow(CheckCol) == Row + (Col - CheckCol) ? false :
  26            getQueenRow(CheckCol) == Row + (CheckCol - Col) ? false :
  27            okRecurse(Row, Col, CheckCol + 1);
  28   }
  29   constexpr bool at(int Row, int Col) const {
  30     return getQueenRow(Col) == Row;
  31   }
  32   constexpr bool check(const char *, int=0, int=0) const;
  33 };
  34
  35 constexpr Board buildBoardRecurse(int N, int Col, const Board &B);
  36 constexpr Board buildBoardScan(int N, int Col, int Row, const Board &B);
  37 constexpr Board tryBoard(const Board &Try,
  38                          int N, int Col, int Row, const Board &B) {
  39   return Try.Failed ? buildBoardScan(N, Col, Row, B) : Try;
  40 }
  41 constexpr Board buildBoardScan(int N, int Col, int Row, const Board &B) {
  42   return Row == N ? Board(0, true) :
  43          B.ok(Row, Col) ?
  44          tryBoard(buildBoardRecurse(N, Col + 1, B.addQueen(Row, Col)),
  45                   N, Col, Row+1, B) :
  46          buildBoardScan(N, Col, Row + 1, B);
  47 }
  48 constexpr Board buildBoardRecurse(int N, int Col, const Board &B) {
  49   return Col == N ? B : buildBoardScan(N, Col, 0, B);
  50 }
  51 constexpr Board buildBoard(int N) {
  52   return buildBoardRecurse(N, 0, Board());
  53 }
  54
  55 constexpr Board q8 = buildBoard(8);
  56
  57 constexpr bool Board::check(const char *p, int Row, int Col) const {
  58   return
  59     *p == '\n' ? check(p+1, Row+1, 0) :
  60     *p == 'o' ? at(Row, Col) && check(p+1, Row, Col+1) :
  61     *p == '-' ? !at(Row, Col) && check(p+1, Row, Col+1) :
  62     *p == 0 ? true :
  63     false;
  64 }
  65 static_assert(q8.check(
  66     "o-------\n"
  67     "------o-\n"
  68     "----o---\n"
  69     "-------o\n"
  70     "-o------\n"
  71     "---o----\n"
  72     "-----o--\n"
  73     "--o-----\n"), "");