HDU 2586 最小公共祖先
2015-11-23 19:59
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How far away ?
Time Limit: 2000/1000 MS (Java/Others) Memory Limit: 32768/32768 K (Java/Others)Total Submission(s): 10005 Accepted Submission(s): 3565
[align=left]Problem Description[/align]
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.
[align=left]Input[/align]
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.
[align=left]Output[/align]
For each test case,output m lines. Each line represents the answer of the query. Output a bland line after each test case.
[align=left]Sample Input[/align]
2
3 2
1 2 10
3 1 15
1 2
2 3
2 2
1 2 100
1 2
2 1
[align=left]Sample Output[/align]
10
25
100
100 #include <iostream>
#include <string.h>
#include <stdio.h>
#include <vector>
using namespace std;
const int N = 50005;
vector<int> v
,w
,query
,num
;
int pre
,dist
,ans
;
bool vis
;
int n;
void Init()
{
for(int i=1; i<=n; i++)
{
v[i].clear();
w[i].clear();
query[i].clear();
num[i].clear();
pre[i] = i;
dist[i] = 0;
vis[i] = false;
}
}
int Find(int x)
{
if(pre[x] != x)
pre[x] = Find(pre[x]);
return pre[x];
}
void Union(int x,int y)
{
x = Find(x);
y = Find(y);
if(x == y) return;
pre[y] = x;
}
void Tarjan(int cur,int val)
{
vis[cur] = true;
dist[cur] = val;
int size = v[cur].size();
for(int i=0;i<size;i++)
{
int tmp = v[cur][i];
if(vis[tmp]) continue;
Tarjan(tmp,val + w[cur][i]);
Union(cur,tmp);
}
int Size = query[cur].size();
for(int i=0;i<Size;i++)
{
int tmp = query[cur][i];
if(!vis[tmp]) continue;
ans[num[cur][i]] = dist[cur] + dist[tmp] - 2*dist[Find(tmp)];
}
}
int main()
{
int T,Q,x,y,z;
scanf("%d",&T);
while(T--)
{
scanf("%d%d",&n,&Q);
Init();
for(int i=1;i<n;i++)
{
scanf("%d%d%d",&x,&y,&z);
v[x].push_back(y);
w[x].push_back(z);
v[y].push_back(x);
w[y].push_back(z);
}
for(int i=0;i<Q;i++)
{
scanf("%d%d",&x,&y);
query[x].push_back(y);
query[y].push_back(x);
num[x].push_back(i);
num[y].push_back(i);
}
Tarjan(1,0);
for(int i=0;i<Q;i++)
printf("%d\n",ans[i]);
}
return 0;
}
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