Leetcode-n-queens

Topic:

The n-queens Puzzle is the problem of placing N Queens on a nxn chessboard such that No, Queens attack.

Given an integer n, return all distinct solutions to the n-queens puzzle.

Each solution contains a distinct board configuration of the n-queens ' placement, where ‘Q‘ and ‘.‘ both Indi Cate a queen and an empty space respectively.

For example,
There exist-distinct solutions to the 4-queens puzzle:

[ [". Q.. ",  //solution 1  " ... Q ",  " Q ... ",".  . Q. "], ["]. Q. ",  //Solution 2  " Q ... ",  " ... Q ",  ". Q.. "]

Ideas:

1) recursion, set the position of the oblique direction to the "Forbidden" area at each recursion

 Packagerecursion;Importjava.util.ArrayList;Importjava.util.List; Public classNqueens { PublicList<list<string>> Solvenqueens (intN) {Char[] board =New Char[N][n];  for(inti = 0; I < n; ++i) { for(intj = 0; J < N; ++j) {Board[i][j]= '. '; }} List<List<String>> res =NewArraylist<list<string>>(); Solve (res,0, board, N); returnRes; }        Private voidSolve (list<list<string>> res,intRowChar[] board,intN) {if(Row >=N) {List<String> record =NewArraylist<string>();  for(inti = 0; I < n; ++i) {StringBuilder sb=NewStringBuilder ();  for(intj = 0; J < N; ++j) {if(board[i][j]! = ' Q ') Board[i][j]= '. ';                Sb.append (Board[i][j]);            } record.add (Sb.tostring ());            } res.add (record); return; }                 for(inti = 0; I < n; ++i) {if(Board[row][i] = = '. ') {                Char[] Cpyboard =Copyboard (board, N);                Setforbiddenarea (Cpyboard, row, I, n); Solve (res, row+ 1, Cpyboard, N); }        }    }        Private voidSetforbiddenarea (Char[] board,intIintJintN) {//Rows and Columns         for(intk = 0; K < n; ++k) {Board[i][k]= ' F '; BOARD[K][J]= ' F '; }        //Diagonal         for(intK = 1-n; K <= n-1; ++k) {if(i + k >= 0 && i + K < n && j + k >= 0 && j + K <N) board[i+ K][j + K] = ' F '; if(i + k >= 0 && i + K < n && j-k >= 0 && J-k <N) board[i+ k][j-k] = ' F '; } Board[i][j]= ' Q '; }        Private Char[] Copyboard (Char[] board,intN) {Char[] Cpyboard =New Char[N][n];  for(inti = 0; I < n; ++i) { for(intj = 0; J < N; ++j) Cpyboard[i][j]=Board[i][j]; }        returnCpyboard; }         Public Static voidMain (string[] args) {//TODO auto-generated Method StubNqueens n =NewNqueens (); List<List<String>> res = N.solvenqueens (4);  for(list<string>subres:res) {             for(String s:subres) System.out.print (s+ "\ T"); System.out.println ("\ n"); }    }}

2) use a one-dimensional array to store the position of Q for each line, I for line I, rows[i] for the position of Q.

 Packagerecursion;Importjava.util.ArrayList;Importjava.util.List; Public classNqueens { PublicList<list<string>> Solvenqueens (intN) {List<List<String>> res =NewArraylist<list<string>>(); int[] positions =New int[n]; Solve (positions, res,0, N); returnRes; }        Private voidSolveint[] positions, list<list<string>> Res,intRowintN) {if(Row = =N) {List<String> record =NewArraylist<string>();  for(inti = 0; I < n; ++i) {StringBuilder sb=NewStringBuilder ();  for(intj = 0; J < N; ++j) Sb.append (‘.‘); Sb.setcharat (Positions[i],' Q ');            Record.add (Sb.tostring ());        } res.add (record); } Else {             for(inti = 0; I < n; ++i) {if(IsValid (positions, row, i)) {Positions[row]=i; Solve (positions, res, row+ 1, N); }            }        }    }        Private BooleanIsValid (int[] positions,intRowintcandidate) {         for(inti = 0; i < row; ++i) {if(Positions[i] = = Candidate | | Math.Abs (i-row) = = Math.Abs (Positions[i]-candidate)) return false; }        return true; }         Public Static voidMain (string[] args) {//TODO auto-generated Method StubNqueens n =NewNqueens (); List<List<String>> res = N.solvenqueens (4);  for(list<string>subres:res) {             for(String s:subres) System.out.print (s+ "\ T"); System.out.println ("\ n"); }    }}

Leetcode-n-queens