codeforces#P1005C. Summarize to the Power of Two
Summarize to the Power of Two
Description
A sequence $a_1, a_2, \dots, a_n$ is called good if, for each element $a_i$, there exists an element $a_j$ ($i \ne j$) such that $a_i+a_j$ is a power of two (that is, $2^d$ for some non-negative integer $d$).
For example, the following sequences are good:
- $[5, 3, 11]$ (for example, for $a_1=5$ we can choose $a_2=3$. Note that their sum is a power of two. Similarly, such an element can be found for $a_2$ and $a_3$),
- $[1, 1, 1, 1023]$,
- $[7, 39, 89, 25, 89]$,
- $[]$.
Note that, by definition, an empty sequence (with a length of $0$) is good.
For example, the following sequences are not good:
- $[16]$ (for $a_1=16$, it is impossible to find another element $a_j$ such that their sum is a power of two),
- $[4, 16]$ (for $a_1=4$, it is impossible to find another element $a_j$ such that their sum is a power of two),
- $[1, 3, 2, 8, 8, 8]$ (for $a_3=2$, it is impossible to find another element $a_j$ such that their sum is a power of two).
You are given a sequence $a_1, a_2, \dots, a_n$. What is the minimum number of elements you need to remove to make it good? You can delete an arbitrary set of elements.
The first line contains the integer $n$ ($1 \le n \le 120000$) — the length of the given sequence.
The second line contains the sequence of integers $a_1, a_2, \dots, a_n$ ($1 \le a_i \le 10^9$).
Print the minimum number of elements needed to be removed from the given sequence in order to make it good. It is possible that you need to delete all $n$ elements, make it empty, and thus get a good sequence.
Input
The first line contains the integer $n$ ($1 \le n \le 120000$) — the length of the given sequence.
The second line contains the sequence of integers $a_1, a_2, \dots, a_n$ ($1 \le a_i \le 10^9$).
Output
Print the minimum number of elements needed to be removed from the given sequence in order to make it good. It is possible that you need to delete all $n$ elements, make it empty, and thus get a good sequence.
Samples
6
4 7 1 5 4 9
1
5
1 2 3 4 5
2
1
16
1
4
1 1 1 1023
0
Note
In the first example, it is enough to delete one element $a_4=5$. The remaining elements form the sequence $[4, 7, 1, 4, 9]$, which is good.