poj 3164 Command Network

链接：http://poj.org/problem?id=3164　　

　　继续最小树形图~

　　这次的最小树形图直接套模板上去就可以了....我把刚才那篇的写法用上去，AC的还是相当顺利的，就只有刚开始打错了几个字，搞到TLE了一下。于是，我确定这种写法（我觉得已经是相当飘逸的了）可以加入我的模板...

　　题意就没必要解释了，这么明显。

#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <cmath>

typedef double ll;

const int maxn = 105;
const ll inf = 1e30;
int pre[maxn], fold[maxn], vis[maxn];
ll cost[maxn], min_cost;

struct edge{
    int b;
    int e;
    ll c;
}E[maxn * maxn];

struct point{
    ll x;
    ll y;
}P[maxn];

ll dis(point a, point b){
    ll dx = a.x - b.x;
    ll dy = a.y - b.y;

    return sqrt(dx * dx + dy * dy);
}

bool make_tree(int root, int v, int e){
    int i, j;
    int s, t, cnt;

    min_cost = 0;
    while (true){
        for (i = 0; i < v; i++){
            cost[i] = 1e31;
        }
        for (i = 0; i < e; i++){
            s = E[i].b;
            t = E[i].e;
            #ifndef ONLINE_JUDGE
            printf("%d %d: %.2f\n", s, t, E[i].c);
            #endif

            if (cost[t] > E[i].c && s != t){
                cost[t] = E[i].c;
                pre[t] = s;
            }
        }
        #ifndef ONLINE_JUDGE
        for (i = 0; i < v; i++)
            printf("%d  pre : %d   in : %.2f\n", i, pre[i], cost[i]);
        puts("");
        #endif
        cost[root] = 0;
        for (i = 0; i < v; i++){
            min_cost += cost[i];
            fold[i] = vis[i] = -1;
            if (cost[i] > inf && i != root) return false;
        }

        cnt = 0;
        for (i = 0; i < v; i++){
            j = i;
            vis[i] = i;
            for (j = pre[j]; j != root && vis[j] != i && fold[i] == -1; j = pre[j]) vis[j] = i;
            if (j == root || fold[j] != -1) continue;
            for (s = j, fold[s] = cnt, s = pre[s]; s != j; s = pre[s]) fold[s] = cnt;
            cnt++;
        }
        if (!cnt) return true;
        for (i = 0; i < v; i++){
            if (fold[i] == -1) fold[i] = cnt++;
        }
        #ifndef ONLINE_JUDGE
        for (i = 0; i < v; i++) printf("fold %d : %d\n", i, fold[i]);
        #endif
        for (i = 0; i < e; i++){
            s = E[i].b;
            t = E[i].e;

            E[i].b = fold[s];
            E[i].e = fold[t];
            if (E[i].b != E[i].e){
                E[i].c -= cost[t];
            }
        }
        v = cnt;
        root = fold[root];
    }
}


bool deal(){
    int n, m;
    int b, e;

    if (scanf("%d%d", &n, &m) == EOF) return false;
    for (int i = 0; i < n; i++){
        scanf("%lf%lf", &P[i].x, &P[i].y);
    }
    for (int i = 0; i < m; i++){
        scanf("%d%d", &b, &e);
        b--; e--;
        E[i].b = b;
        E[i].e = e;
        E[i].c = dis(P[b], P[e]); // coordinate transform
    }
    if (make_tree(0, n, m)){
        printf("%.2f\n", min_cost);
    }
    else puts("poor snoopy");

    return true;
}

int main(){
    #ifndef ONLINE_JUDGE
    freopen("in", "r", stdin);
    #endif
    while (deal());

    return 0;
}

——written by Lyon