# "Leetcode" N-queens

Source: Internet
Author: User

Test instructions

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

N Queen problem, but to output each solution. Just give each line a recursive go.

Code

C++:

`Class Solution {public:vector<vector<string> > Solvenqueens (int n) {/* Initialize vector variable, number of I represents line I        The Queen in which column */vector<int> chess (n,-1);        /* Save Results */vector< vector<string> > ans;        /* Solve the problem */Solvequeen (0,n,chess.begin (), ans);    return ans;        } void Solvequeen (int r,int n,vector<int>::iterator chess,vector< vector<string> > &ans) { /*r equals n When each row has a queen * * if (r = = N) {/*solution is used to hold a legal solution */vector<string> Solu            tion;            for (int i = 0;i < N;++i) {Solution.push_back (getrowinstring (n,*));            } ans.push_back (solution);        Return            }/* To see which column of the current row can be put Queen */for (int i = 0;i < N;++i) {* (chess+r) = i;             /* Check legality */if (check (chess,r,n)) {/* down recursion */Solvequeen (R+1,n,chess,ans); }        }/* Check for conflicts */bool Check (Vector<int>::iterator chess,int r,int N) {/* for each previous line */For        (int i = 0;i < R;++i)            {/* Calculates the distance between two columns */int dis = ABS (* (CHESS+R)-* (Chess+i));        /* dis = 0 in the same column, dis = r-1 constitutes isosceles triangle, i.e. diagonal */if (dis = = 0 | | dis = = r-i) return false;    } return true;        }/* Constructs n-length string getrowinstring (int n,int col) in Col for Queen, {string str (n, '. ');        Str.replace (col,1, "Q");    return str; }};`
Python:

`Class solution:    # @return An integer    def solvenqueens (self, N):        Self.array = [0 for I in range (0,n)] self        . Ans = []        self.solve (0,n)        return Self.ans    def solve (self,r,n):        if r = = N:            solution = [] for            i in RA Nge (0,n):                row = ['. ' For x in range (0,n)]                row[self.array[i]] = ' Q '                solution.append (". Join (Row))            Self.ans.append (solution)            del solution            return for        I in range (0,n):            self.array[r] = i            if Self.check (r,n):                self.solve (r+1,n)    def check (self,r,n): For        I in range (0,r):            dis = ABS ( SELF.ARRAY[R]-self.array[i])            if dis = = 0 or dis = = r-i:                return False        return True`

"Leetcode" N-queens

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