Codeforces 716D - Complete The Graph（最短路）

  1 #include <iostream>
  2 #include <queue>
  3 #include <stack>
  4 #include <cstdio>
  5 #include <vector>
  6 #include <map>
  7 #include <set>
  8 #include <bitset>
  9 #include <algorithm>
 10 #include <cmath>
 11 #include <cstring>
 12 #include <cstdlib>
 13 #include <string>
 14 #include <sstream>
 15 #include <time.h>
 16 #define x first
 17 #define y second
 18 #define pb push_back
 19 #define mp make_pair
 20 #define lson l,m,rt*2
 21 #define rson m+1,r,rt*2+1
 22 #define mt(A,B) memset(A,B,sizeof(A))
 23 #define mod 1000000007
 24 using namespace std;
 25 typedef long long LL;
 26 const double PI = acos(-1);
 27 const int N=30000+10;
 28 const int inf = 0x3f3f3f3f;
 29 //const LL INF=0x3f3f3f3f3f3f3f3fLL;
 30 const LL INF=1e15;
 31 struct node
 32 {
 33     int u,v,next;
 34     LL w;
 35 } E[N];
 36 int n,m,s,t,top=0,head[N];
 37 LL L,dis[N];
 38 bool vis[N];
 39 vector<node> P;
 40 void add(int u,int v,LL w)
 41 {
 42     E[top].u=u;
 43     E[top].v=v;
 44     E[top].w=w;
 45     E[top].next=head[u];
 46     head[u]=top++;
 47 }
 48 struct Node//堆优化的dij所用的结构体
 49 {
 50     int v;//点
 51     LL d;//距离
 52     Node(int v=0,LL d=0):v(v),d(d) {}//我也不懂为什么这样写，反正照写就对了
 53     bool operator <(const Node &r)const
 54     {
 55         return d>r.d;
 56     }
 57 };
 58 void dij()
 59 {
 60     for(int i=0; i<N; i++)//先初始化
 61     {
 62         dis[i]=INF;
 63         vis[i]=false;
 64     }
 65     dis[s]=0;
 66     priority_queue<Node> Q;
 67     Q.push(Node(s,0));
 68     while(!Q.empty())
 69     {
 70         Node p=Q.top();
 71         Q.pop();
 72         if(vis[p.v])continue;
 73         vis[p.v]=true;
 74         for(int i=head[p.v]; i!=-1; i=E[i].next)
 75         {
 76             int v=E[i].v;
 77             if(!vis[v]&&dis[v]>dis[p.v]+E[i].w)//松弛法
 78             {
 79                 dis[v]=dis[p.v]+E[i].w;
 80                 Q.push(Node(v,dis[v]));
 81             }
 82         }
 83     }
 84 }
 85 int main()
 86 {
 87 #ifdef Local
 88     freopen("data.txt","r",stdin);
 89 #endif
 90     int u,v;
 91     LL w;
 92     mt(head,-1);//邻接表初始化
 93     cin>>n>>m>>L>>s>>t;
 94     for(int i=0; i<m; i++)//先将节点分类，w!=0的先加进去建图
 95     {
 96         cin>>u>>v>>w;
 97         if(w)
 98         {
 99             add(u,v,w);
100             add(v,u,w);
101         }
102         else
103         {
104             node p;
105             p.u=u;
106             p.v=v;
107             p.w=w;
108             p.next=-1;
109             P.pb(p);
110         }
111     }
112     dij();
113     if(dis[t]<L)
114     {
115         puts("NO");
116     }
117     else if(dis[t]==L)
118     {
119         puts("YES");
120         for(int i=0; i<top; i+=2)
121         {
122             printf("%d %d %I64d\n",E[i].u,E[i].v,E[i].w);
123         }
124         for(int i=0; i<P.size(); i++)
125         {
126             printf("%d %d %I64d\n",P[i].u,P[i].v,INF);
127         }
128     }
129     else
130     {
131         int pos=0,flag=0;
132         for(pos=0; pos<P.size(); pos++)
133         {
134             add(P[pos].u,P[pos].v,1);
135             add(P[pos].v,P[pos].u,1);
136             dij();
137             if(dis[t]<=L)
138             {
139                 E[top-1].w+=L-dis[t];
140                 E[top-2].w+=L-dis[t];
141                 flag=1;
142                 break;
143             }
144         }
145         if(!flag)puts("NO");
146         else
147         {
148             puts("YES");
149             for(int i=0; i<top; i+=2)
150             {
151                 printf("%d %d %I64d\n",E[i].u,E[i].v,E[i].w);
152             }
153             for(int i=pos+1; i<P.size(); i++)
154             {
155                 printf("%d %d %I64d\n",P[i].u,P[i].v,INF);
156             }
157         }
158     }
159 #ifdef Local
160     cerr << "time: " << (LL) clock() * 1000 / CLOCKS_PER_SEC << " ms" << endl;
161 #endif
162 }