#include <bits/stdc++.h>
using namespace std;
#define int long long int
#define double long double
inline int power(int a, int b) {
int x = 1;
while (b) {
if (b & 1) x *= a;
a *= a;
b >>= 1;
}
return x;
}
const int M = 1000000007;
const int N = 3e5+9;
const int INF = 2e9+1;
const int LINF = 2000000000000000001;
//_ ***************************** START Below *******************************
vector<int> a;
void consistency(int n, int k) {
unordered_map<int,int> mp;
int ans = 0;
for(int i=0; i<n; i++){
if(mp.count(a[i] + k)){
ans += mp[a[i]+k];
}
mp[a[i]]++;
}
cout << ans << endl;
}
void solve() {
a = {1, 5, 3, 4, 2};
int n = a.size();
int k = 2;
consistency(n, k) ;
}
int32_t main() {
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
int t = 1;
while (t--) {
solve();
}
return 0;
}
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