from typing import Dict, List
def main():
n: int = 0
x: int = 0
ans: int = 0
m = dict()
n = int(input().strip())
arr: List[str] = input().strip().split(' ')
arr: List[int] = [*map(int, arr)]
for i in range(0, n):
x = arr[i]
for j in range(0, 31):
key: int = pow(2, j) - x
if key in m:
ans += m[key]
else:
ans += 0
if x not in m:
m[x] = 0
m[x] += 1
print(ans)
main()
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
int main()
{
int n; scanf("%d", &n);
vector<int> a(n + 1);
for (int i = 1; i <= n; i++)
scanf("%d", &a[i]);
ll ans = 0;
for (int j = 1; j <= 30; j++)
{
map<int, int> mp;
for (int i = 1; i <= n; i++)
{
int val = (1 << j);
if (val - a[i] != 0 && mp.count(val - a[i])) ans += mp[val - a[i]];
mp[a[i]]++;
}
}
printf("%lld\n", ans);
return 0;
}
/*
1, 2, 3, 4, 5, 6
*/21. Merge Two Sorted Lists | 203. Remove Linked List Elements |
733. Flood Fill | 206. Reverse Linked List |
83. Remove Duplicates from Sorted List | 116. Populating Next Right Pointers in Each Node |
145. Binary Tree Postorder Traversal | 94. Binary Tree Inorder Traversal |
101. Symmetric Tree | 77. Combinations |
46. Permutations | 226. Invert Binary Tree |
112. Path Sum | 1556A - A Variety of Operations |
136. Single Number | 169. Majority Element |
119. Pascal's Triangle II | 409. Longest Palindrome |
1574A - Regular Bracket Sequences | 1574B - Combinatorics Homework |
1567A - Domino Disaster | 1593A - Elections |
1607A - Linear Keyboard | EQUALCOIN Equal Coins |
XOREQN Xor Equation | MAKEPAL Weird Palindrome Making |
HILLSEQ Hill Sequence | MAXBRIDGE Maximise the bridges |
WLDRPL Wildcard Replacement | 1221. Split a String in Balanced Strings |