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Add solution for N-Queen problem which uses bit-operation

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Still uses DFS, optimized for state compression.

Signed-off-by: Hanlin Shi <shihanlin9@gmail.com>
This commit is contained in:
Hanlin Shi
2021-05-31 00:43:43 -07:00
parent ad3dfff270
commit cff768e63c
1 changed files with 45 additions and 35 deletions
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80
leetcode/0051.N-Queens/51. N-Queens.go
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@ -48,38 +48,48 @@ func generateBoard(n int, row *[]int) []string {
}
// 解法二 二进制操作法
// class Solution
// {
// int n;
// string getNq(int p)
// {
// string s(n, '.');
// s[p] = 'Q';
// return s;
// }
// void nQueens(int p, int l, int m, int r, vector<vector<string>> &res)
// {
// static vector<string> ans;
// if (p >= n)
// {
// res.push_back(ans);
// return ;
// }
// int mask = l | m | r;
// for (int i = 0, b = 1; i < n; ++ i, b <<= 1)
// if (!(mask & b))
// {
// ans.push_back(getNq(i));
// nQueens(p + 1, (l | b) >> 1, m | b, (r | b) << 1, res);
// ans.pop_back();
// }
// }
// public:
// vector<vector<string> > solveNQueens(int n)
// {
// this->n = n;
// vector<vector<string>> res;
// nQueens(0, 0, 0, 0, res);
// return res;
// }
// };
func solveNQueens2(n int) (res [][]string) {
placements := make([]string, n)
for i := range placements {
buf := make([]byte, n)
for j := range placements {
if i == j {
buf[j] = 'Q'
} else {
buf[j] = '.'
}
}
placements[i] = string(buf)
}
var construct func(prev []int)
construct = func(prev []int) {
if len(prev) == n {
plan := make([]string, n)
for i := 0; i < n; i++ {
plan[i] = placements[prev[i]]
}
res = append(res, plan)
return
}
occupied := 0
for i := range prev {
dist := len(prev) - i
bit := 1 << prev[i]
occupied |= bit | bit<<dist | bit>>dist
}
prev = append(prev, -1)
for i := 0; i < n; i++ {
if (occupied>>i)&1 != 0 {
continue
}
prev[len(prev)-1] = i
construct(prev)
}
}
construct(make([]int, 0, n))
return
}