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466C - Number of Ways.cpp
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466C - Number of Ways.cpp
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#include <bits/stdc++.h>
using namespace std;
//string s;
//getline(cin, s);
typedef long long ll;
typedef pair<int, int> pii;
typedef unsigned long ull;
typedef vector<pii> vii;
typedef vector<int> vi;
typedef pair<int, int> ii;
typedef priority_queue<int> maxPq;
typedef priority_queue<ll, vector<ll>, greater<ll> > minPq;
typedef deque<int> dq;
#define F first
#define S second
#define PB push_back
#define MP make_pair
#define forVar(type, var, init, till, increment) for (type var = init; var < till; var += increment)
#define deb(x) cout << x << endl;
#define MAX 5 * 10000 + 1
#define INF 10000000000
#define endl '\n'
int n;
ll ai;
ll sums[500100];
ll apps[500100];
int main()
{
//freopen("input.txt", "r", stdin);
//freopen("output.txt", "w", stdout);
cin >> n;
cin >> ai;
sums[0] = ai;
for(int i = 1; i < n; ++i)
{
cin >> ai;
sums[i] += sums[i-1] + ai;
}
if (sums[n-1] % 3LL)
{
cout << 0 << endl;
return 0;
}
ll obj = sums[n-1] / 3LL;
if (sums[0] == obj) apps[0] = 1;
for(int i = 1; i < n; ++i)
{
apps[i] = apps[i-1];
if (sums[i] == obj) apps[i] = apps[i] + 1;
}
ll contar = 0;
for(int i = 1; i < n-1; ++i)
{
if (sums[i] == obj*2) contar += apps[i-1];
}
cout << contar << endl;
return 0;
}