Description
There are n houses in the village and some bidirectional roads connecting them. Every day peole always like to ask like this "How far is it if I want to go from house A to house B"? Usually it hard to answer. But luckily int this village the answer is always unique, since the roads are built in the way that there is a unique simple path("simple" means you can't visit a place twice) between every two houses. Yout task is to answer all these curious people.
Input
First line is a single integer T(T<=10), indicating the number of test cases.
For each test case,in the first line there are two numbers n(2<=n<=40000) and m (1<=m<=200),the number of houses and the number of queries. The following n-1 lines each consisting three numbers i,j,k, separated bu a single space, meaning that there is a road connecting house i and house j,with length k(0<k<=40000).The houses are labeled from 1 to n.
Next m lines each has distinct integers i and j, you areato answer the distance between house i and house j.
For each test case,in the first line there are two numbers n(2<=n<=40000) and m (1<=m<=200),the number of houses and the number of queries. The following n-1 lines each consisting three numbers i,j,k, separated bu a single space, meaning that there is a road connecting house i and house j,with length k(0<k<=40000).The houses are labeled from 1 to n.
Next m lines each has distinct integers i and j, you areato answer the distance between house i and house j.
Output
For each test case,output m lines. Each line represents the answer of the query. Output a bland line after each test case.
Sample Input
2
3 2
1 2 10
3 1 15
1 2
2 3
2 2
1 2 100
1 2
2 1
Sample Output
10
25
100
100
终于知道Lca还有那么一个需要注意的地方，上一篇不知道为什么没有栈溢出，这个溢出了，原来是我的Lca是先算距离，那样会dfs很多次，应该直接Lca，下面两个代码，第一个溢出，第二个AC 31ms
#include<map> #include<set> #include<stack> #include<queue> #include<cmath> #include<vector> #include<cstdio> #include<string> #include<cstring> #include<cstdlib> #include<iostream> #include<algorithm> #define inf 0x0f0f0f0f using namespace std; const int maxn=40000+10; struct node { int c,v; }; vector<node>tree[maxn],que[maxn]; int num[maxn],dis[maxn],father[maxn]; bool mark[maxn],vis[maxn]; void init(int n) { for (int i=0;i<=n;i++) { tree[i].clear(); que[i].clear(); num[i]=0; vis[i]=0; mark[i]=0; father[i]=i; dis[i]=0; } } int find(int x) { return x==father[x]?x:father[x]=find(father[x]); } void Lca(int u) { father[u]=u; for (int i=0;i<tree[u].size();i++) { int v=tree[u][i].v; if (!mark[v]) { mark[v]=true; dis[v]=dis[u]+tree[u][i].c; Lca(v); father[v]=u; } } vis[u]=true; for (int i=0;i<que[u].size();i++) { int v=que[u][i].v; if (vis[v]) { num[que[u][i].c]=dis[u]+dis[v]-2*dis[find(v)]; } } } int main() { int t,n,m,x,y,c; scanf("%d",&t); while (t--) { scanf("%d%d",&n,&m); init(n); for (int i=1;i<n;i++) { scanf("%d%d%d",&x,&y,&c); node temp; temp.c=c; temp.v=y; tree[x].push_back(temp); temp.v=x; tree[y].push_back(temp); } for (int i=0;i<m;i++) { scanf("%d%d",&x,&y); node temp; temp.v=y; temp.c=i; que[x].push_back(temp); temp.v=x; que[y].push_back(temp); } mark[1]=true; Lca(1); for (int i=0;i<m;i++) { printf("%d ",num[i]); } //printf(" "); } return 0; }
#include<map> #include<set> #include<stack> #include<queue> #include<cmath> #include<vector> #include<cstdio> #include<string> #include<cstring> #include<cstdlib> #include<iostream> #include<algorithm> #define inf 0x0f0f0f0f using namespace std; const int maxn=40000+10; struct node { int c,v; }; vector<node>tree[maxn],que[maxn]; int num[maxn],dis[maxn],father[maxn]; bool vis[maxn]; void init(int n) { for (int i=0;i<=n;i++) { tree[i].clear(); que[i].clear(); num[i]=0; vis[i]=0; father[i]=i; dis[i]=0; } } int find(int x) { return x==father[x]?x:father[x]=find(father[x]); } void Lca(int u) { father[u]=u; vis[u]=true; for (int i=0;i<que[u].size();i++) { int v=que[u][i].v; if (vis[v]) { num[que[u][i].c]=dis[u]+dis[v]-2*dis[find(v)]; } } for (int i=0;i<tree[u].size();i++) { int v=tree[u][i].v; if (!vis[v]) { dis[v]=dis[u]+tree[u][i].c; Lca(v); father[v]=u; } } } int main() { int t,n,m,x,y,c; scanf("%d",&t); while (t--) { scanf("%d%d",&n,&m); init(n); for (int i=1;i<n;i++) { scanf("%d%d%d",&x,&y,&c); node temp; temp.c=c; temp.v=y; tree[x].push_back(temp); temp.v=x; tree[y].push_back(temp); } for (int i=0;i<m;i++) { scanf("%d%d",&x,&y); node temp; temp.v=y; temp.c=i; que[x].push_back(temp); temp.v=x; que[y].push_back(temp); } Lca(1); for (int i=0;i<m;i++) { printf("%d ",num[i]); } //printf(" "); } return 0; }