[Leetcode]51 N-queens

https://oj.leetcode.com/problems/n-queens/

http://blog.csdn.net/linhuanmars/article/details/20667175

public class solution {    public list<string[]>  Solvenqueens (int n)  {                 List<String[]> result = new ArrayList<> ();         int[] qcols = new int[n];         solve (N, 0, qcols, result);         return result;            }         private void solve (Int n, // number of queen                         int row, // current row iteration, [0 ->  n-1]                        int[] qcols, // describing queens positions                        List< String[]> result)     {        if  (row  == n)         {             // all [0, n-1] has fulfilled, a solution  found.            result.add (ToBoard (Qcols)) ;            return;         }                 // we&nbSp;are on row        // try to put q  in each columns, and check        for  ( int i = 0 ; i < n ; i ++)          {            qcols[row] =  i;            boolean valid =  checkboard (Qcols, row);             if   (valid)             {                 // enter next iteration                 solve (n,  Row + 1, qCols, result);            }         }    }        //   This method checks to see if the new Q (ROW) is in line with the existing board     //  because one row only holds the position of a Q, so the line must conform to     //   Check column:qcols[i] != qcols[row]    //  check diagonal  abs (I - row)  != abs (Qcols[i] - qcols[row])     // check new q (on  row)  can fit existing board.    private boolean  Checkboard (Int[] qcols, int row)     {         for  (int i = 0 ; i < row ; i ++)          {             if  (QCOLS[I]&NBSP;==&NBsp;qcols[row])  | |                math.abs (i -  row)  == math.abs (qcols[i] - qcols[row))                 return false;         }        return true;    }     // Build the board.        private  String[] toboard (Int[] qcols)     {         int n = qcols.length;        string[] b  = new String[n];        for  (int i =  0 ; i < n ; i ++)         {             int qcol = qcols[i];             StringBuilder sb = new  StringBuilder ();            for  (int j  = 0 ; j < qcol ; j ++)                  sb.append (".");             sb.append ("Q");             for  (int j = qcol + 1  ; j < n ; j ++)                  sb.append (".");             b[i] = sb.tostring ();         }        return b;     }}

[Leetcode]51 N-queens