CF1188B
对于类似的题尝试把一个式子和两个有关化简为只和一个有关
题意：
给出n, p, k，接下来给出n个数，要你寻找有多少对i j 满足题中式子
思路：
所以只要遍历i，通过map记录即可
// Decline is inevitable,
// Romance will last forever.
//#include <bits/stdc++.h>
#include <iostream>
#include <cmath>
#include <cstring>
#include <string>
#include <cstdio>
#include <algorithm>
#include <queue>
#include <stack>
#include <map>
#include <set>
#include <deque>
#include <vector>
using namespace std;
#define mst(a, x) memset(a, x, sizeof(a))
#define INF 0x3f3f3f3f
//#define mp make_pair
#define pb push_back
#define pii pair<int,int>
#define fi first
#define se second
#define ll long long
#define int long long
const int maxn = 2e5 + 10;
const int maxm = 1e3 + 10;
const int P = 1e4 + 7;
map<int, int> mp;
int n, p, k;
int f(int x) {
return x * x % p * x % p * x % p;
}
void solve() {
mp.clear();
int ans = 0;
cin >> n >> p >> k;
for(int i =1; i <= n; i++) {
int x;
cin >> x;
if(mp[(f(x)-x*k%p+p)%p]) {
ans += mp[(f(x)-x*k%p+p)%p];
}
mp[(f(x)-x*k%p+p)%p]++;
}
cout << ans << endl;
}
signed main() {
ios::sync_with_stdio(false); cin.tie(0); cout.tie(0);
// int T; scanf("%d", &T); while(T--)
// freopen("1.txt","r",stdin);
// freopen("output.txt","w",stdout);
// int T; cin >> T;while(T--)
solve();
return 0;
}