LeetCode-37-Sudoku Solver， list转字符串join，回溯

class Solution(object):    count=0    ans=[[0 for x in range(9)]for y in range(9)]    def solveSudoku(self, board):        """        :type board: List[List[str]]        :rtype: void Do not return anything, modify board in-place instead.        """        B=[[0 for x in range(9)]for y in range(9)]        for i in range(9):            for j in range(9):                if board[i][j]=='.':continue                B[i][j]=ord(board[i][j])-ord('0')        for i in range(9):            for j in range(9):                if B[i][j] == 0:                    flag=self.dfs(B, i, j)                    if flag:                        #board=B                        self.copyBoard(board,B)                        #print B                        #print board                        return                    break    def copyBoard(self,board,B):        for i in range(9):            for j in range(9):                B[i][j]=chr(ord("0")+B[i][j])        for i in range(9):            board[i]="".join(B[i])    def dfs(self, B, x, y):        for num in range(1, 10):            B[x][y] = num            if self.judgePoint(B, x, y) == False:                B[x][y] = 0                continue            nextx = x            nexty = y            while nextx < 9:                nexty = nexty + 1                if nexty == 9:                    nexty = 0                    nextx += 1                    if nextx == 9: return True                if B[nextx][nexty] == 0:                    break            flag=self.dfs(B, nextx, nexty)            if flag:                return True            B[x][y] = 0        return False    def judgePoint(self, board, x, y):        area = 0        for i in range(9):            if i!=y and board[x][i]==board[x][y]:return False            if i!=x and board[i][y]==board[x][y]:return False            px = x / 3 * 3 + i / 3            py = y / 3 * 3 + i - i / 3 * 3            c = board[px][py]            if c == 0: continue            num = c            if area & (1 << num) != 0:                return False            area |= 1 << num        return True