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#include "leetcode.h"
class Solution {
public:
vector<vector<string>> solveNQueens(int n) {
vector<vector<string>> ans;
vector<string> nQueens(n, string(n, '.'));
solve(ans, nQueens, 0, n);
return ans;
}
private:
void solve(vector<vector<string>> &ans, vector<string> &nQueens, int row,
int &n) {
if (row == n) {
ans.push_back(nQueens);
return;
}
for (int col = 0; col != n; ++col)
if (isValid(nQueens, row, col, n)) {
nQueens[row][col] = 'Q';
solve(ans, nQueens, row + 1, n);
nQueens[row][col] = '.';
}
}
bool isValid(vector<string> &nQueens, int row, int col, int &n) {
// check if col had queen
for (int i = 0; i != row; ++i)
if (nQueens[i][col] == 'Q')
return false;
// check if 45deg diagonal had queen
for (int i = row - 1, j = col - 1; i >= 0 && j >= 0; --i, --j)
if (nQueens[i][j] == 'Q')
return false;
// check if 135deg diagonal had queen
for (int i = row - 1, j = col + 1; i >= 0 && j < n; --i, ++j)
if (nQueens[i][j] == 'Q')
return false;
return true;
}
};
int main() {}
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