Leetcode-n-queens

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.. "]

Has you met this question in a real interview? Analysis:how to determine whether the current position on jth row is valid? Suppose jth row position is place[j] and ith row position is place[i]. Then we found this place[i] leads three positions at jth row invalid. They is place[i], place[i]+j-i, place[i]-(j-i). Solution:

1  Public classSolution {2      PublicList<string[]> Solvenqueens (intN) {3list<string[]> res =NewArraylist<string[]>();4         int[] Place =New int[n];5Arrays.fill (place,-1);6         intLevel = 0;7   8          while(Level!=-1){9             if(level>=N) {Ten constructres (place,res,n); Onelevel--; A                 Continue; -             } -  the             intval =Place[level]; -val++; -              while(val<N) { -                 Booleanvalid =true; +                  for(inti=0;i<level;i++) -                     if(Val==place[i] | | val==place[i]+level-i | | val==place[i]-(level-i)) { +valid =false; A                          Break; at                     } -                 if(valid) Break; -                 Elseval++; -             } -  -             if(val<N) { inplace[level]=Val; -level++; to}Else { +Place[level]=-1; -level--; the             } *         } $ Panax Notoginseng         returnRes; -          the     } +  A      Public voidConstructres (int[] Place, list<string[]> Res,intN) { the         Char[] line =New Char[n]; +Arrays.fill (line, '. ')); -string[] Oneres =NewString[n]; $          for(inti=0;i<n;i++){ $             intval =Place[i]; -line[val]= ' Q '; -String Linestr =NewString (line); theLine[val]= '. '; -oneres[i]=Linestr;Wuyi         } the Res.add (oneres); -     }        Wu}

Leetcode-n-queens