Educational Codeforces Round 54 (Rated for Div. 2) D Edge Deletion (SPFA + bfs)

  1 #include<iostream>
  2 #include<algorithm>
  3 #include<cstring>
  4 #include<vector>
  5 #include<queue>
  6 #include<map>
  7 using namespace std;
  8 typedef long long LL;
  9 typedef pair<LL,LL> P;
 10 const int maxn = 3e5+10;
 11 const LL INF = 1e18;
 12 vector<int>ans;
 13 int n, m, k;
 14 struct node{
 15     LL to,cost;
 16     node() {}
 17     node(LL a, LL b) :to(a), cost(b) {}
 18 };
 19 vector<node> e[maxn];
 20 LL vis[maxn], f[maxn], dis[maxn];
 21 map<P,LL>mp;
 22 void SPFA(int s)
 23 {
 24     for (int i = 0; i < maxn; i++) {
 25         vis[i] = 0; f[i] = 0;
 26         dis[i] = INF;
 27     }
 28     dis[s] = 0;
 29     vis[s] = 1; f[s]++;
 30     queue<int>Q;
 31     Q.push(s);
 32     while (!Q.empty()) {
 33         int t = Q.front(); Q.pop();
 34         vis[t] = 0;
 35         for (int i = 0; i < e[t].size(); i++) {
 36             LL tmp = e[t][i].to;
 37             if (dis[tmp] > dis[t] + e[t][i].cost) {
 38                 dis[tmp] = dis[t] + e[t][i].cost;
 39                 if (!vis[tmp]) {
 40                     vis[tmp] = 1;
 41                     Q.push(tmp);
 42                     if (++f[tmp] > n)return;
 43                 }
 44             }
 45         }
 46     }
 47     return;
 48 }
 49 void BFS(LL x)
 50 {
 51     ans.clear();
 52     queue<node>Q;
 53     memset(vis,0,sizeof(vis));
 54     Q.push(node(x,0));
 55     vis[x] = 1;
 56     while(!Q.empty()&&ans.size()<k){
 57         node dep = Q.front();Q.pop();
 58         for(int i=0;i<e[dep.to].size();i++){
 59             LL to = e[dep.to][i].to;
 60             if(ans.size()>n-1&&ans.size()<k){
 61                 ans.push_back(mp[make_pair(dep.to,to)]);
 62                 continue;
 63             }
 64             if(ans.size()==k)return;
 65             if(vis[to])continue;
 66             if((dep.cost+e[dep.to][i].cost)>dis[to])continue;
 67             ans.push_back(mp[make_pair(dep.to,to)]);
 68             vis[to] = 1;
 69             Q.push(node(to,dep.cost+e[dep.to][i].cost));
 70             if(ans.size()==k)return;
 71         }
 72     }
 73 }
 74 int main()
 75 {
 76     ios::sync_with_stdio(false);
 77     while (cin >> n >> m >> k) {
 78         mp.clear();
 79         for(int i=1;i<=n;i++)e[i].clear();
 80         for (LL a, b, c, i = 1; i <= m; i++) {
 81             cin >> a >> b >> c;
 82             e[a].push_back(node(b, c));
 83             e[b].push_back(node(a, c));
 84             mp[make_pair(a,b)] = i;
 85             mp[make_pair(b,a)] = i;
 86             // cout<<mp[make_pair(a,b)]<<endl;
 87         }
 88         if(k==0){
 89             cout<<"0"<<endl;
 90             continue;
 91         }
 92         SPFA(1);
 93         BFS(1);
 94         cout<<ans.size()<<endl;
 95         for(int i=0;i<ans.size()-1;i++)
 96             cout<<ans[i]<<" ";
 97         cout<<ans[ans.size()-1]<<endl;
 98     }
 99     return 0;
100 }