Codeforces Round #558 (Div. 2) B. Cat Party(思维)

#include <bits/stdc++.h>
#define ll long long
#define maxn 100005
using namespace std;
ll pre[maxn];
int n;

int main()
{
	scanf("%d", &n);
	map<ll,ll> a, b;
	for(int i=0;i<n;i++){
		scanf("%lld", &pre[i]);
	}
	ll ans = 0;
	ll pos = 0;
	for(int i=0;i<n;i++){
		a[pre[i]] ++;
		b[a[pre[i]]] ++;
		if(a[pre[i]] != 1) b[a[pre[i]] - 1] --;
		if(pos < a[pre[i]]) pos = a[pre[i]];
		if(i + 1 == b[1]) ans = i + 1;
		if(b[1] == 1 && i + 1 == 1 + b[pos] * pos) ans = i + 1;
		if(b[pos] == 1 && i + 1 == b[pos - 1] * (pos - 1) + pos) ans = i + 1;
	}
	printf("%lld\n", ans);
	return 0;
}