f[i][j]表示钱i个字符中未配对的j个，if s[i]=='(',f[i][j] = f[i-1][j-1],if s[i]==')',f[i][j] = f[i-1][j+1] if s[i]=='?'，则两种都维护，根据代码实际情况对ij进行单独判断