left=getLeft(data,k)

right=getRight(data,k)

retun right-left+1

getLeft data,k

    left=0

    right=arr.length-1

    mid=left+(right-left)/2

    while  left<=right

        if arr[mid]<k    //关键

            left=mid+1

        else

            right=mid-1

        mid=left+(right-left)/2

    return left

getRight data,k

    left=0

    right=arr.length-1

    mid=left+(right-left)/2

    while  left<=right

        if arr[mid]<=k   //关键

            left=mid+1

        else

            right=mid-1

        mid=left+(right-left)/2

    return right