Constructing Roads(spfa)
http://acm.sdut.edu.cn/sdutoj/problem.php?action=showproblem&problemid=2493
1 #include <stdio.h> 2 #include <string.h> 3 #include <queue> 4 using namespace std; 5 const int maxn=1010; 6 const int maxm=maxn*maxn; 7 const long long INF=1LL<<60; 8 int vis[maxn],head[maxn]; 9 int n,m,cnt = 0; 10 struct node 11 { 12 int u,v; 13 long long w; 14 int next; 15 16 } edge[maxm]; 17 18 inline void add(int u,int v,long long w) 19 { 20 edge[cnt].u = u; 21 edge[cnt].v = v; 22 edge[cnt].w = w; 23 edge[cnt].next = head[u]; 24 head[u] = cnt++; 25 } 26 27 void spfa(int s, long long dis[]) 28 { 29 30 queue<int>q; 31 q.push(s); 32 vis[s] = 1; 33 dis[s] = 0; 34 while(!q.empty()) 35 { 36 int u = q.front(); 37 q.pop(); 38 vis[u] = 0; 39 for (int j = head[u]; j!=-1; j= edge[j].next) 40 { 41 int v = edge[j].v; 42 long long w = edge[j].w; 43 if (dis[u]+w < dis[v]) 44 { 45 dis[v] = dis[u]+w; 46 q.push(v); 47 vis[v] = 1; 48 } 49 } 50 } 51 52 } 53 void init() 54 { 55 56 } 57 int main() 58 { 59 int u,v; 60 long long w; 61 long long dis1[maxn],dis2[maxn]; 62 while(~scanf("%d %d",&n,&m)) 63 { 64 for (int i = 0; i <= n; i++) 65 { 66 vis[i] = 0; 67 dis1[i] = INF; 68 dis2[i] = INF; 69 head[i] = -1; 70 } 71 cnt = 0; 72 for (int i = 0; i < m; i++) 73 { 74 scanf("%d %d %lld",&u,&v,&w); 75 add(u,v,w); 76 add(v,u,w); 77 } 78 int s,e; 79 long long min=INF; 80 scanf("%d %d",&s,&e); 81 spfa(s,dis1);//求出起点到所有点的最短路径 82 spfa(e,dis2);//求出终点到所有点的最短路径 83 for (int i = 0; i < cnt; i++)//遍历所有的边 84 { 85 u = edge[i].u; 86 v = edge[i].v; 87 w = edge[i].w; 88 if (dis1[u]+dis2[v]+w/2 < min)//S->u+e->v+w/2即为改变后的权值，找出最小的 89 min = dis1[u]+dis2[v]+w/2; 90 } 91 if(min==INF) 92 { 93 puts("No solution"); 94 continue; 95 } 96 printf("%lld\n",min); 97 } 98 return 0; 99 }
