Submission #104769

#	Time	Username	Problem	Language	Result	Execution time	Memory
104769		puyu_liao	Duathlon (APIO18_duathlon)	C++14	0 / 100	132 ms	13148 KiB

count_triplets

#include<bits/stdc++.h>
#include<stdint.h>
using namespace std;
#define IOS {cin.tie(0);ios_base::sync_with_stdio(false);}
#define N 300005
#define int int64_t

vector<int> v[N];
int sz[N];
int ans = 0,sum;

void dfs(int x,int p){
	sz[x] = 1;
	for(int i : v[x]) if(i != p){
		dfs(i,x);
		sz[x] += sz[i];
	}
}

void dfs2(int x,int p,int sp){
	int cnt = v[x].size();
	for(int i : v[x]) if(i != p){
		dfs2(i,x,sz[x]-sz[i]);
		if(cnt>1)ans += sz[i] * (sum - sz[i] - 1);
	}
	if(cnt > 1) ans += sp * (sum - sp - 1);
}

int32_t main(){
	IOS;
	int n,m,a,b;
	cin >> n >> m;
	for(int i=0;i<m;i++){
		cin >> a >> b;
		v[a].push_back(b);
		v[b].push_back(a);
	}
	if(m!=n-1) return 0;
	dfs(1,1);
	//for(int i=1;i<=n;i++) cout << sz[i] << '\n';
	sum = sz[1];
	dfs2(1,1,0);
	cout << ans << '\n';
	return 0;
}

• Subtask 1: 0 / 5
• Subtask 2: 0 / 11
• Subtask 3: 0 / 8
• Subtask 4: 0 / 10
• Subtask 5: 0 / 13
• Subtask 6: 0 / 15
• Subtask 7: 0 / 20
• Subtask 8: 0 / 8
• Subtask 9: 0 / 10