New Exercise

Exercise/Homework7/Q2KahTuoPuAOE.cpp

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+#include <iostream>
+#include <vector>
+#include <queue>
+#include <algorithm>
+
+using namespace std;
+
+int main(){
+    int n, m;
+    while(cin >> n >> m) {
+        vector<vector<pair<int, int>>> adj(n + 1);
+        vector<int> degree(n + 1, 0);
+        vector<pair<pair<int, int>, int>> edges;
+        queue<int> q;
+        vector<int> topo;
+        vector<int> ve(n + 1, 0);
+        for(int i = 0; i < m; i++) {
+            int a, b, w;
+            cin >> a >> b >> w;
+            a--; b--;
+            adj[a].push_back(make_pair(b, w));
+            degree[b]++;
+            edges.push_back(make_pair(make_pair(a, b), w));
+        }
+        for(int i = 0; i < n; i++) {
+            if(degree[i] == 0) {
+                q.push(i);
+            }
+        }
+        while(!q.empty()) {
+            int u = q.front();
+            q.pop();
+            topo.push_back(u);
+            for(auto [v, w] : adj[u]) {
+                degree[v]--;
+                if(degree[v] == 0) {
+                    q.push(v);
+                }
+            }
+        }
+        //topo为拓扑排序
+        if(topo.size() != n) {
+            cout << "unworkable project" << endl;
+            continue;
+        }
+        //正向一次，求出最早开始时间
+        for(int i = 0; i < topo.size(); i++) {
+            int u = topo[i];
+            for(auto [v, w] : adj[u]) {
+                ve[v] = max(ve[v], ve[u] + w);
+            }
+        }
+        int max_ve = 0;
+        for(int i = 0; i < n; i++) {
+            max_ve = max(max_ve, ve[i]);
+        }
+        //反向一次，求出最晚开始时间
+        vector<int> vl(n + 1, max_ve);
+        for(int i = topo.size() - 1; i >= 0; i--) {
+            int u = topo[i];
+            for(auto [v, w] : adj[u]) {
+                vl[u] = min(vl[u], vl[v] - w);
+            }
+        }
+
+        cout << max_ve << endl;
+
+        //判断是否关键路径
+        vector<pair<int, int>> is_critical;
+        for(auto e : edges) {
+            int a = e.first.first;
+            int b = e.first.second;
+            int w = e.second;
+            if(ve[a] + w == vl[b]) {
+                is_critical.push_back(make_pair(a, b));
+            }
+        }
+        sort(is_critical.begin(), is_critical.end());
+        for(auto [a, b] : is_critical) {
+            a++; b++;
+            cout << a << "->" << b << endl;
+        }
+    }
+
+    return 0;
+}