2024广东省赛 I.不等式

题目

#include <bits/stdc++.h>
using namespace std;
#define int long long

#define pb push_back

#define fi first

#define se second

#define lson p << 1

#define rson p << 1 | 1

#define ll long long

const int maxn = 1e6 + 5, inf = 1e9, maxm = 4e4 + 5, base = 37;
const int N = 4e3;
const int mod = 1e9 + 7;
// const int mod = 998244353;
// const __int128 mod = 212370440130137957LL;

int n, m;
int a[maxn];

//long long ? maxn ? n? m?
void solve(){
    ll res = 0;
    cin >> n >> m;
    vector<vector<int>> G(n + 1);
    vector<vector<pair<int, int>>> req(n + 1);
    vector<int> ind(n + 1), f(n + 1, 1);
    for(int i = 1; i <= m; i++){
        int x, y, z;
        cin >> x >> y >> z;
        G[y].pb(x);
        G[z].pb(x);
        ind[x] += 2;
        req[x].pb({y, z});
    }
    int cnt = 0;
    queue<int> q;
    for(int i = 1; i <= n; i++){
        if(ind[i] == 0){
            q.push(i);
            cnt++;
            f[i] = 1;
        }
    }
    while(!q.empty()){
        int u = q.front();
        q.pop();
        for(auto [x, y] : req[u]){
            f[u] = max(f[u], f[x] + f[y]);
        }
        res += f[u];
        if(res > inf){
            cout << -1 << '\n';
            return;
        }
        for(auto v : G[u]){
            ind[v]--;
            if(ind[v] == 0){
                q.push(v);
                cnt++;
            }
        }
    }
    if(cnt != n){
        cout << -1 << '\n';
        return;
    }
    cout << res << '\n';
}
    
signed main(){
    ios::sync_with_stdio(0);
    cin.tie(0);

    cout << fixed << setprecision(9);
    int T = 1;
    // cin >> T;
    while (T--)
    {
        solve();
    }
    return 0;
}

原文地址：https://blog.csdn.net/way_back__/article/details/139302585

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