52. N-Queens II

class Solution {
    public int totalNQueens(int n) {
        int[][] board=new int[n][n];
        return totalNQueens(0, board);
    }
    private int totalNQueens(int i, int[][] board)
    {
        if(i==board.length)
            return 1;
        int ret=0;
        for(int j=0;j<board.length;j++)
            if(board[i][j]==0)
            {
                board[i][j]=1;
                fillQueuePath(i, j, board, -1);
                ret+=totalNQueens(i+1,board);
                fillQueuePath(i, j, board, 1);
                board[i][j]=0;
            }
        return ret;
    }
    private void fillQueuePath(int i, int j, int[][] board, int val){
        for(int k=1;i+k<board.length;k++)
        {
            board[i+k][j]+=val;
            if(j-k>=0)
                board[i+k][j-k]+=val;
            if(j+k<board.length)
                board[i+k][j+k]+=val;
        }
    }    
}

class Solution {
    public int totalNQueens(int n) {
        boolean[] cols=new boolean[n];
        boolean[] d1=new boolean[n*2];
        boolean[] d2=new boolean[n*2];
        return totalNQueens(0, cols, d1, d2);
    }
    private int totalNQueens(int i, boolean[] cols, boolean[] d1, boolean[] d2)
    {
        if(i==cols.length)
            return 1;
        int ret=0;
        for(int j=0;j<cols.length;j++)
        {
            int dn1=i-j+cols.length;
            int dn2=i+j;
            if(cols[j]==false&&d1[dn1]==false&&d2[dn2]==false)
            {
                cols[j]=true;
                d1[dn1]=true;
                d2[dn2]=true;
                ret+=totalNQueens(i+1,cols, d1, d2);
                cols[j]=false;
                d1[dn1]=false;
                d2[dn2]=false;
            }
        }
        return ret;
    }
}