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最小树形图 UVA 11183 Teen Girl Squad

2014-05-02 18:10 309 查看

Problem I

Teen Girl Squad

Input: Standard Input
Output: Standard Output

-- 3 spring rolls please.

-- MSG'D!!

-- Oh! My stomach lining!

Strong Bad
You are part of a group of n teenage girls armed with cellphones. You have some news you want to tell everyone in the group. The problem is that no two of you are in the same room, and you must communicate using
only cellphones. What's worse is that due to excessive usage, your parents have refused to pay your cellphone bills, so you must distribute the news by calling each other in the cheapest possible way. You will call several of your friends, they will call some
of their friends, and so on until everyone in the group hears the news.
Each of you is using a different phone service provider, and you know the price of girl A calling girl B for all possible A and B. Not all of your friends like each other, and some of them will never call people they don't like.
Your job is to find the cheapest possible sequence of calls so that the news spreads from you to all n-1 other members of the group.
Input
The first line of input gives the number of cases, N (N<150). N test cases follow. Each one starts with two lines containing n (0<=n<=1000)and m (0
<= m <= 40,000). Girls are numbered from 0 to n-1, and you are girl 0. The next m lines will each contain 3 integers, u, v and w, meaning
that a call from girl u to girl v costs w cents (0 <= w <= 1000). No other calls are possible because of grudges, rivalries and because they are, like, lame. The input file size
is around 1200 KB.

Output

For each test case, output one line containing "Case #x:" followed by the cost of the cheapest method of distributing the news. If there is no solution, print "Possums!" instead.

Sample Input Output for Sample Input

0 1 10

1 0 10

0 1 10

0 2 10

1 3 20

2 3 30

0 1 10

1 2 20

2 0 30

2 3 100

Case #1: 10

Case #2: Possums!

Case #3: 40

Case #4: 130

Problem setter: Igor Naverniouk

题意：。。。以0为根的最小树形图。

思路：。。。我比较懒，就模仿一下别人的题解吧：最小树形图模板题。 =_=||

代码：

#include<iostream>
#include<cstdio>
#include<cstring>
#include<string.h>
#include<algorithm>
#include<vector>
using namespace std;
const int maxn = 1500 + 5;
const int inf = 1e6;
int n, m;
struct Edge
{
int u, v;
int cost;
Edge() { }
Edge(int f, int t, int c)
:u(f), v(t), cost(c) { }
};
vector<Edge> edges;
int id[maxn];
int in[maxn], pre[maxn];
int vis[maxn];

void input()
{
scanf("%d%d", &n, &m);
edges.clear();
for (int i = 0; i < m; ++i) {
int u, v, w; scanf("%d%d%d", &u, &v, &w);
//--u, --v;
if (v==0 || u==v) continue;
edges.push_back(Edge(u, v, w));
}
}

int DMST(int root)
{
int ret = 0;
while (true) {
fill(in, in + n, inf);
for (int i = 0; i < edges.size(); ++i) {
int u = edges[i].u, v = edges[i].v;
if (u == v || in[v]<=edges[i].cost) continue;
pre[v] = u; in[v] = edges[i].cost;
}
for (int i = 0; i < n; ++i) {
if (i == root) continue;
if (in[i] == inf) return -1;
ret += in[i];
}
int cnt = 0; memset(id, -1, sizeof(id));
memset(vis, -1, sizeof(vis));
for (int i = 0; i < n; ++i) {
int v = i;
while (vis[v] != i&&id[v] == -1 && v != root)
{
vis[v] = i;
v = pre[v];
}
if (vis[v] == i) {
for (int u = pre[v]; u != v; u = pre[u])
id[u] = cnt;
id[v] = cnt++;
}
}
if (cnt == 0) break;
for (int i = 0; i < n;++i)
if (id[i] == -1) id[i] = cnt++;
for (int i = 0; i < edges.size(); ++i) {
int u = edges[i].u, v = edges[i].v;
edges[i].u = id[u];
edges[i].v = id[v];
if (id[u] == id[v]) continue;
edges[i].cost -= in[v];
}
root = id[root];
n = cnt;
}
return ret;
}

void solve()
{
int sum = DMST(0);
if (sum == -1) puts("Possums!");
else printf("%d\n", sum);
}

int main()
{
int T; cin >> T;
int Cas = 0;
while (T--) {
input();
printf("Case #%d: ", ++Cas);
solve();
}
}

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