uva 11183 - Teen Girl Squad（有向生成树）

题目链接：uva 11183 - Teen Girl Squad

#include <cstdio>
#include <cstring>
#include <vector>
#include <algorithm>

using namespace std;
typedef long long ll;
const int inf = 0x3f3f3f3f;
const int maxn = 1005;

struct DMST {
struct Edge {
int u, v, d;
Edge(int u = 0, int v = 0, int d = 0): u(u), v(v), d(d) {}
bool operator < (const Edge& u) const { return d < u.d; }
};

int in[maxn], pre[maxn], id[maxn], vis[maxn];
vector<Edge> edges;

void init () { edges.clear(); }
void addEdge(int u, int v, int d) { edges.push_back(Edge(u, v, d)); }

bool directedMST(int root, int n, int& ans) {
ans = 0;

while (true) {
// 删除自环+找最小入边
memset(in, inf, sizeof(in));
for (int i = 0; i < edges.size(); i++) {
int u = edges[i].u, v = edges[i].v;
if (edges[i].d < in[v] && u != v) {
pre[v] = u;
in[v] = edges[i].d;
}
}

// 判断是否可以到达所有节点
for (int i = 0; i < n; i++) {
if (i == root) continue;
if (in[i] == inf) return false;
}

int cntnode = 0;
//memset(id, -1, sizeof(int) * n);
//memset(vis, -1, sizeof(int) * n);
memset(id, -1, sizeof(id));
memset(vis, -1, sizeof(vis));
in[root] = 0;

for (int i = 0; i < n; i++) {
ans += in[i];
int v = i;
while (vis[v] != i && id[v] == -1 && v != root) {
vis[v] = i;
v = pre[v];
}
if (v != root && id[v] == -1) {
for (int u = pre[v]; u != v; u = pre[u])
id[u] = cntnode;
id[v] = cntnode++;
}
}

// 没有找到环, 终止
if (cntnode == 0) break;

// 缩点，重新标记
for (int i = 0; i < n; i++) {
if (id[i] == -1)
id[i] = cntnode++;
}

for (int i = 0; i < edges.size(); i++) {
int v = edges[i].v;
edges[i].u = id[edges[i].u];
edges[i].v = id[edges[i].v];
if (edges[i].u != edges[i].v)
edges[i].d -= in[v];
}
n = cntnode;
root = id[root];
}
return true;
}
}solver;

int main () {
int cas, n, m, u, v, w;
scanf("%d", &cas);
for (int kcas = 1; kcas <= cas; kcas++) {
solver.init();
scanf("%d%d", &n, &m);
for (int i = 0; i < m; i++) {
scanf("%d%d%d", &u, &v, &w);
solver.addEdge(u, v, w);
}
int ans;
if (solver.directedMST(0, n, ans))
printf("Case #%d: %d\n", kcas, ans);
else
printf("Case #%d: Possums!\n", kcas);
}
return 0;
}