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B.cpp
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B.cpp
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#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
using namespace std;
#define pb push_back
#define ppb pop_back
#define mp make_pair
#define lb lower_bound
#define ub upper_bound
#define ff first
#define ss second
#define rep(i, a, b) for(int i = a; i < b; i++)
#define repR(i, a, b) for(int i = a; i >= b; --i)
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define sz(x) (int)(x).size()
#define mem0(a) memset(a,0,sizeof(a))
#define mem1(a) memset(a,-1,sizeof(a))
typedef long long ll;
typedef unsigned long long ull;
typedef long double lld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
#define MOD1 1000000007
#define MOD2 998244353
#define INF 2000000000000000000
#define ps(x,y) fixed << setprecision(y) << x
#define fastio ios_base::sync_with_stdio(false),cin.tie(NULL),cout.tie(NULL)
template <typename T> using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
//member functions :
//1. order_of_key(k) : number of elements strictly lesser than k
//2. find_by_order(k) : k-th element in the set
/*---------------------------------------------------------Debugging----------------------------------------------------------*/
#ifndef ONLINE_JUDGE
#define debug(x) cerr << #x <<" "; _print(x); cerr << endl;
#else
#define debug(x)
#endif
void _print(int t) {cerr << t;}
void _print(ll t) {cerr << t;}
void _print(char t) {cerr << t;}
void _print(string t) {cerr << t;}
void _print(double t) {cerr << t;}
void _print(lld t) {cerr << t;}
void _print(ull t) {cerr << t;}
template <class T, class V> void _print(pair <T, V> p);
template <class T> void _print(vector <T> v);
template <class T> void _print(set <T> v);
template <class T, class V> void _print(map <T, V> v);
template <class T> void _print(multiset <T> v);
template <class T, class V> void _print(pair <T, V> p) {cerr << "{"; _print(p.ff); cerr << ","; _print(p.ss); cerr << "}";}
template <class T> void _print(vector <T> v) {cerr << "[ "; for (T i : v) {_print(i); cerr << " ";} cerr << "]";}
template <class T> void _print(set <T> v) {cerr << "[ "; for (T i : v) {_print(i); cerr << " ";} cerr << "]";}
template <class T> void _print(multiset <T> v) {cerr << "[ "; for (T i : v) {_print(i); cerr << " ";} cerr << "]";}
template <class T, class V> void _print(map <T, V> v) {cerr << "[ "; for (auto i : v) {_print(i); cerr << " ";} cerr << "]";}
/*----------------------------------------------------------------------------------------------------------------------------*/
void solve()
{
vector<ll> powers(40);
powers[0] = 1;
for (int i = 1; i < 40; i++) {
powers[i] = powers[i - 1] * 2LL;
}
int n;
cin >> n;
vector<ll> a(n);
map<ll, vector<int>> m;
rep(i, 0, n) {
cin >> a[i];
m[a[i]].pb(i);
}
ll ans = 0;
rep(i, 0, n) {
for (auto x : powers) {
ll j = x - a[i];
if (m.count(j)) {
ans += sz(m[j]) - (ub(all(m[j]), i) - m[j].begin());
}
}
}
cout << ans << '\n';
}
int main()
{
#ifndef ONLINE_JUDGE
//freopen("input.txt", "r", stdin);
//freopen("output.txt", "w", stdout);
freopen("Error.txt", "w", stderr);
#endif
fastio;
int t = 1;
//cin >> t;
while (t--) solve();
return 0;
}