LeetCode OJ N-Queens II

Follow up for N-Queens problem.

Now, instead outputting board configurations, return the total number of distinct solutions.

follow up the question N queens.

class Solution {  public:    int totalNQueens(int n) {        return solveNQueens(n).size();    }    vector<vector<string> > solveNQueens(int n) {        NLine = n;        w = n;        h = n;        for (int i = 0; i < h; i++) {            for (int j = 0; j < w; j++) {                chessBoard[i][j] = '.';            }        }        ans.clear();  // notice that this class may be used to solve a question more than one time        DFS(0);        return ans;    }    void DFS(int nowLine) {        if (nowLine == NLine) {  // have got the answer            writeIn();            return;        }        for (int j = 0; j < NLine; j++) {            if (isValid(nowLine, j)) {                chessBoard[nowLine][j] = 'Q';                DFS(nowLine + 1);                chessBoard[nowLine][j] = '.';            }        }    }    bool isValid(int i, int j) {  // to judge if a position is valid to put a queen        for (int k = 0; k < w; k++) {            if (chessBoard[i][k] == 'Q') return false;  // from left to right            if (chessBoard[k][j] == 'Q') return false;  // from up to down        }        for (int k = 0; k < h; k++) {            if (inBoard(i + 1 * k, j + 1 * k) && chessBoard[i + 1 * k][j + 1 * k] == 'Q') return false;  // from leftUp to rightDown            if (inBoard(i - 1 * k, j - 1 * k) && chessBoard[i - 1 * k][j - 1 * k] == 'Q') return false;  // from rightDown to leftUp            if (inBoard(i - 1 * k, j + 1 * k) && chessBoard[i - 1 * k][j + 1 * k] == 'Q') return false;  // from leftDown to rightUp            if (inBoard(i + 1 * k, j - 1 * k) && chessBoard[i + 1 * k][j - 1 * k] == 'Q') return false;  // from rightUp to leftDown        }        return true;    }    bool inBoard(int i, int j) {        return 0 <= i && i < h && 0 <= j && j < w;    }    void writeIn() {        vector<string> ansPart;        for (int i = 0; i < h; i++) {            string temp;            for (int j = 0; j < w; j++) {                temp.push_back(chessBoard[i][j]);            }            ansPart.push_back(temp);        }        ans.push_back(ansPart);    }  private:    char chessBoard[16][16];    int NLine;    int w, h;    vector<vector<string> > ans;};