算法——图论——关键活动

原题

#include <iostream>
#include <vector>
#include <queue>
#include <set>

using namespace std;

struct edge {
    int destination;
    int dist;

    edge(int destination_, int dist_) : destination(destination_), dist(dist_) {}
};

vector<edge> graph[100];
vector<edge> reGraph[100];
vector<int> inDo(100, 0);
vector<int> outDo(100, 0);
vector<int> lessTime(100, 0);
vector<int> moreTime(100, 0x3fffffff);

int main() {

    int n, m;
    cin >> n >> m;
    for (int i = 0; i < m; ++i) {
        int u, v, w;
        cin >> u >> v >> w;
        graph[u].emplace_back(v, w);
        reGraph[v].emplace_back(u, w);
        outDo[u]++;
        inDo[v]++;
    }
    queue<int> q;
    for (int i = 0; i < n; ++i) {
        if (inDo[i] == 0) {
            q.push(i);
            lessTime[i] = 0;
        }
    }

    while (!q.empty()) {
        int cur = q.front();
        q.pop();

        for (edge neighbor: graph[cur]) {
            inDo[neighbor.destination]--;
            lessTime[neighbor.destination] = max(lessTime[neighbor.destination], lessTime[cur] + neighbor.dist);
            if (inDo[neighbor.destination] == 0) {
                q.push(neighbor.destination);
            }
        }
    }

    int totalTime = 0;
    for (int i = 0; i < n; ++i) {
        if (inDo[i] != 0) {
            cout << "No" << endl;
            return 0;
        }
        totalTime = max(totalTime, lessTime[i]);
    }

    for (int i = 0; i < n; ++i) {
        if (outDo[i] == 0) {
            q.push(i);
            moreTime[i] = totalTime;
        }
    }


    while (!q.empty()) {
        int cur = q.front();
        q.pop();

        for (edge neighbor: reGraph[cur]) {
            outDo[neighbor.destination]--;
            moreTime[neighbor.destination] = min(moreTime[neighbor.destination], moreTime[cur] - neighbor.dist);
            if (outDo[neighbor.destination] == 0) {
                q.push(neighbor.destination);
            }
        }
    }

    set<pair<int, int>> s;
    for (int i = 0; i < n; ++i) {
    for (edge neighbor: graph[i]) {
        if (moreTime[neighbor.destination] - lessTime[i] - neighbor.dist == 0) {
            s.insert({i, neighbor.destination});
        }
    }
}

//    for (int i = 0; i < n; ++i) {
//        if (lessTime[i] == 0 && moreTime[i] == 0) {
//            q.push(i);
//        }
//    }

//    while (!q.empty()) {
//        auto cur = q.front();
//        q.pop();

//        for (auto neighbor: graph[cur]) {
//            if (lessTime[neighbor.destination] == moreTime[neighbor.destination]) {
//                s.insert({cur, neighbor.destination});
//            q.push(neighbor.destination);
//            }
//        }
//    }

    cout << "Yes" << endl;
    for (auto p: s) {
        cout << p.first << " " << p.second << endl;
    }
    return 0;
}