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