Description
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Input
.gif)
Output
.gif)
Sample Input
6 7
1 2 1
2 3 1
3 4 2
4 5 1
5 6 1
1 3 3
4 6 3
1 6
4
1 2
1 3
4 3
6 5
1 2 1
2 3 1
3 4 2
4 5 1
5 6 1
1 3 3
4 6 3
1 6
4
1 2
1 3
4 3
6 5
Sample Output
7
6
Infinity
7
HINT
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题解：
这和tjoi的桥几乎无差别。。。
传送门：http://www.cnblogs.com/chenyushuo/p/5121234.html
补：此题样例有误，答案为5其实是6
code：
1 #include<cstdio> 2 #include<iostream> 3 #include<cmath> 4 #include<cstring> 5 #include<algorithm> 6 #define maxn 200005 7 #define maxm 400005 8 #define mod 236897 9 #define inf 4557430888798830399LL 10 using namespace std; 11 typedef long long int64; 12 char ch; 13 bool ok; 14 void read(int &x){ 15 for (ok=0,ch=getchar();!isdigit(ch);ch=getchar()) if (ch=='-') ok=1; 16 for (x=0;isdigit(ch);x=x*10+ch-'0',ch=getchar()); 17 if (ok) x=-x; 18 } 19 int n,m,q,a,b,s,t,u[maxm],v[maxm],c[maxm]; 20 int tot=1,now[maxn],son[maxm],pre[maxm],val[maxm]; 21 void put(int a,int b,int c){pre[++tot]=now[a],now[a]=tot,son[tot]=b,val[tot]=c;} 22 int siz,pos[maxn],path[maxn]; 23 int64 dis[maxn][2]; 24 bool bo[maxn],flag[maxm]; 25 struct Heap{ 26 int num; 27 int64 val; 28 }heap[maxn]; 29 void heap_swap(Heap &a,Heap &b){swap(pos[a.num],pos[b.num]),swap(a,b);} 30 void up(int son){ 31 int fa=son>>1; 32 while (fa){ 33 if (heap[fa].val<=heap[son].val) break; 34 heap_swap(heap[fa],heap[son]); 35 son=fa,fa>>=1; 36 } 37 } 38 void down(){ 39 int fa=1,son=fa<<1; 40 while (son<=siz){ 41 if (son+1<=siz&&heap[son+1].val<heap[son].val) son++; 42 if (heap[fa].val<=heap[son].val) break; 43 heap_swap(heap[fa],heap[son]); 44 fa=son,son<<=1; 45 } 46 } 47 void dijkstra(int s,int op){ 48 memset(bo,0,sizeof(bo)); 49 memset(pos,0,sizeof(pos)); 50 siz=0; 51 heap[++siz]=(Heap){s,0},pos[s]=siz; 52 for (;siz;){ 53 int u=heap[1].num; 54 int64 d=heap[1].val; 55 bo[u]=1,dis[u][op]=d,heap_swap(heap[1],heap[siz--]),down(); 56 for (int p=now[u],v=son[p];p;p=pre[p],v=son[p]) 57 if (!bo[v]){ 58 if (!pos[v]){ 59 heap[++siz]=(Heap){v,d+val[p]},pos[v]=siz,up(pos[v]); 60 if (!op) path[v]=p; 61 } 62 else if (heap[pos[v]].val>d+val[p]){ 63 heap[pos[v]].val=d+val[p],up(pos[v]); 64 if (!op) path[v]=p; 65 } 66 } 67 } 68 } 69 int cnt,tmp[maxn],list[maxn],dep[maxn]; 70 void prepare(){ 71 for (int u=t;u;u=son[path[u]^1]) tmp[++cnt]=u; 72 for (int i=1;i<=cnt;i++) list[cnt-i+1]=tmp[i]; 73 for (int i=1;i<=cnt;i++) dep[list[i]]=i; 74 for (int i=1;i<=n;i++) if (!dep[i]){ 75 int u=i,d=0; 76 while (!dep[u]) u=son[path[u]^1]; 77 d=dep[u],u=i; 78 while (!dep[u]) dep[u]=d,u=son[path[u]^1]; 79 } 80 for (int u=1;u<=n;u++) if (path[u]) flag[path[u]>>1]=1; 81 } 82 int64 dam[maxn]; 83 struct seg{ 84 #define ls k<<1 85 #define rs (k<<1)+1 86 int64 cov[maxn<<2]; 87 void init(){memset(cov,63,sizeof(cov));} 88 void modify(int k,int l,int r,int x,int y,int64 v){ 89 if (l==x&&r==y){cov[k]=min(cov[k],v);return;} 90 int m=(l+r)>>1; 91 if (y<=m) modify(ls,l,m,x,y,v); 92 else if (x<=m) modify(ls,l,m,x,m,v),modify(rs,m+1,r,m+1,y,v); 93 else modify(rs,m+1,r,x,y,v); 94 } 95 void query(int k,int l,int r,int64 ans){ 96 ans=min(ans,cov[k]); 97 if (l==r){dam[l]=ans;return;} 98 int m=(l+r)>>1; 99 query(ls,l,m,ans),query(rs,m+1,r,ans); 100 } 101 }T; 102 void work(int u,int v,int c){ 103 if (dep[u]==dep[v]) return; 104 if (dep[u]>dep[v]) swap(u,v); 105 T.modify(1,1,cnt-1,dep[u],dep[v]-1,dis[u][0]+c+dis[v][1]); 106 } 107 int main(){ 108 read(n),read(m); 109 for (int i=1;i<=m;i++) read(u[i]),read(v[i]),read(c[i]),put(u[i],v[i],c[i]),put(v[i],u[i],c[i]); 110 read(s),read(t); 111 dijkstra(s,0),dijkstra(t,1); 112 prepare(),T.init(); 113 for (int i=1;i<=m;i++) if (!flag[i]) work(u[i],v[i],c[i]); 114 T.query(1,1,cnt-1,inf); 115 for (read(q);q;q--){ 116 read(a),read(b); 117 if (dis[a][0]>dis[b][0]) swap(a,b); 118 if (dep[a]+1==dep[b]&&son[path[b]^1]==a){ 119 if (dam[dep[a]]!=inf) printf("%lld ",dam[dep[a]]); 120 else puts("Infinity"); 121 } 122 else{ 123 if (dis[t][0]!=inf) printf("%lld ",dis[t][0]); 124 else puts("Infinity"); 125 } 126 } 127 return 0; 128 }