第九周作业2

// A code block
func grayCode(n int) []int {    
    res := []int{0}      
      for cur := 0; cur < n; cur++ {       
           length := len(res)         
              for i := length - 1; i >= 0; i-- { //对之前的格雷码进行逆序并高位补1              
                res = append(res, res[i] + (1 << cur))            }   
                     }        return res 
                        }