Starting with x and repeatedly multiplying by x,
we can compute x31 with thirty multiplications:
<!-- MATH
$x2 = x \times x$
-->
x2 = x x x,
<!-- MATH
$x3 = x2 \times x$
-->
x3 = x2 x x,x4 = x3 x x,
... ,
<!-- MATH
$x{31} = x{30}\times x$
-->x31 = x30 x x.
x2 = x x x, x3 = x2 x x, x6 = x3 x x3, x7 = x6 x x, x14 = x7 x x7,
x15 = x14 x x, x30 = x15 x x15, x31 = x30 x x.
This is not the shortest sequence of multiplications to compute x31.
There are many ways with only seven multiplications.
The following is one of them:
<!-- MATH
$x2 = x \times x$
-->
x2 = x x x,x4 = x2 x x2,
<!-- MATH
$x8 = x4 \times x4$
-->
x8 = x4 x x4,x10 = x8 x x2,
<!-- MATH
$x{20} = x{10} \times x{10}$
-->
x20 = x10 x x10,x30 = x20 x x10,
<!-- MATH
$x{31} = x{30} \times x$
-->
x31 = x30 x x.
If division is also available, we can find a shorter sequence of operations. It is possible to compute x31 with six operations (five multiplications and one division):
x2 = x x x, x4 = x2 x x2, x8 = x4 x x4, x16 = x8 x x8, x32 = x16 x x16, x31 = x32 รท x.This is one of the most efficient ways to compute x31 if a division is as fast as a multiplication.
Your mission is to write a program to find the least number of operations to compute xn by multiplication and division starting with x for the given positive integer n. Products and quotients appearing in the sequence of operations should be x to a positive integer's power. In other words, x-3, for example, should never appear.
The input is a sequence of one or more lines each containing
a single integer n.
n is positive and less than or equal to 1000.
The end of the input is indicated by a zero.
Your program should print the least total number of multiplications
and divisions required to compute xn starting with x for the
integer n. The numbers should be written each in a separate line
without any superfluous characters such as leading or trailing spaces.
1 31 70 91 473 512 811 953 0
0 6 8 9 11 9 13 12
Migrated from old NTUJ.
ICPC 2006 Yokohama
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