N-Queens -51

class Solution {
    public boolean isSafe(int row,int col,char[][]board){
        for(int j=0;j<board.length;j++){
            if(board[row][j]=='Q'){
                return false;
            }
        }
        
        for(int i=0;i<board.length;i++){
            if(board[i][col]=='Q'){
                return false;
            }
        }
        
        int r = row;
        for(int c=col;c>=0 && r>=0 ; c--,r--){
            if(board[r][c]=='Q'){
                return false;
            }
        }
        
        r=row;
        for(int c=col;c<board.length && r>=0;r--,c++){
            if(board[r][c]=='Q'){
                return false;
            }
        }
        
        r=row;
        for(int c=col; c>=0 && r<board.length; r++,c--){
            if(board[r][c]=='Q'){
                return false;
            }
        }
         
       //lower right
       for(int c=col; c<board.length && r<board.length; c++, r++) {
           if(board[r][c] == 'Q') {
               return false;
           }
       }

        return true;
    }
    
    public void saveBoard(char[][]board, List<List<String>> allBoard){
        String row="";
        List<String> newBoard = new ArrayList<>();
        
        for(int i=0;i<board.length;i++){
            row="";
            for(int j=0;j<board[0].length;j++){
                if(board[i][j]=='Q')
                    row += 'Q';
                else
                    row += '.';
            }
            newBoard.add(row);
        }
        allBoard.add(newBoard);
    }
    public void solve(char [][]board,List<List<String>> allBoard ,int col){
        if(col==board.length){
            saveBoard(board,allBoard);
            return;
        }
        
        for(int row=0;row<board.length;row++){
            if(isSafe(row,col,board)){
                board[row][col]='Q';
                solve(board,allBoard,col+1);
                board[row][col]= '.';
            }
        }
    }
    public List<List<String>> solveNQueens(int n) {
        List<List<String>> allBoard = new ArrayList();
        char[][]board = new char[n][n];
        solve(board,allBoard,0);
        return allBoard;
        }
}