void QueenPuzzle::placeQueen$($int i$)\{//1.$ you need to implement this function using back$-$tracking $//2.$ when a solution is obtained, please invoke printOut$()$ to display it $//3.$ you need to call IsValid$()$ to determine whether you can legally place a queen in the current cell $//4.$ you need to use placeQueen$()$ to place a queen on the keyboard$\}$int QueenPuzzle::IsValid$($int n$)\{//$compare the queen n withe privous n$-1$ queens to test whether the current place is workable return $1$; $//1$ means no conflict $\}$int main$()\{$ QueenPuzzle queen; queen.placeQueen$(0)$;$\}$