Submission #68126409

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Source Code Expand

#include <bits/stdc++.h>
using namespace std;
#define int long long
#define endl '\n'
#define vec vector
#define fir first
#define sec second
#define pb push_back
typedef long long ll;
typedef pair<int, int> pii;
typedef unsigned long long ull;
const int mod = 998244353;
const int N = 200005;
const int inf = 0x3f3f3f3f3f3f3f3f;
int a[N],cnt[900005];
void Thirstarfish()
{
    int n,ans=0;
    cin>>n;
    for(int i=1;i<=n;i++)
        cin>>a[i];
    for(int i=1;i<=n;i++)
        cnt[i-a[i]+400005]++;
    for(int i=1;i<=n;i++)
        ans+=cnt[a[i]+i+400005];
    cout<<ans<<endl;
}

signed main()
{
        ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    int _ = 1;
    // cin >> _;  //如果是单测记得注释掉这一行
    while (_--)
        Thirstarfish();
    return 0;
}

/*
 things to check
 1.  int overflow or long long memory need
 2.  recursion/array/binary search/dp/loop bounds
 3.  precision
 4.  special cases(n=1,bounds)
 5.  delete debug statements
 6.  initialize(especially multi-tests)
 7.  = or == , n or m ,++ or -- , i or j , > or >= , < or <=
 8.  keep it simple and stupid
 9.  do not delete, use // instead
 10. operator priority
 11. is there anything extra to output?
 12. ...


  something to think about
  1. greedy? dp? searching? dp with matrix/ segment tree? binary search?
  2. If contains "not", why not ?????? or few affect?

  */

Submission Info

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