HDU 4679 terrorist ' s destroy (edge removal + tree diameter)

To a tree, each edge has a weight, remove any edge of the tree, divided into two sub-trees, the longest path of two subtree and the weight on the edge of the multiplication, to a product. Ask to remove that edge to make the product smallest.

First find the longest road on the tree, then there are two cases when you delete the edge:

1. This side is not the longest road side

2. This edge is the edge of the longest road

For the first case, it is easy to calculate the Chuyang product.

For the second case, it is only possible to calculate the longest path length within the two subtree that is divided, which can be preprocessed. Analysis can be found, in this case, the longest path of the two subtrees tree, must be the entire tree of the longest path of the two endpoints as the starting point, so only need to preprocess all points to two endpoints distance, and then according to the longest roadside removed to find the maximum number of two subtrees.

All preprocessing is DFS ...

My Code:

#pragma COMMENT (linker, "/stack:102400000,102400000") #include <cstdio> #include <cstring> #include <
Algorithm> using namespace std;
#define N 100100 int n;
int head[n],cnt,len,ans,id;
int dis_s[n],dis_t[n],mx_s[n],mx_t[n]; struct Edge {int next,to,w,id;}
E[N*2];
    void Add_edge (int a,int b,int w,int id) {e[cnt].id=id;
    E[cnt].to=b;
    E[cnt].w=w;
    E[cnt].next=head[a];
head[a]=cnt++;
        } void Dfs (int u, int fa, int dis[]) {for (int i = head[u]; I! =-1; i = e[i].next) {int v=e[i].to;
    if (V!=FA) {Dis[v]=dis[u]+1;dfs (V,u,dis);}
    }} void Get_max (int u, int fa, int mx[],int dis[]) {mx[u]=dis[u];
        for (int i = head[u]; I! =-1; i = e[i].next) {int v=e[i].to;
            if (V!=FA) {Get_max (V,u,mx,dis);
        Mx[u]=max (Mx[u],mx[v]);
        }}}} void Dfs2 (int u, int fa) {for (int i = head[u]; I! =-1; i = e[i].next) {int v=e[i].to;
if (V!=FA) {            int W;
            if (Dis_s[u]+dis_t[v]+1==len) W=e[i].w*max (Mx_s[u],mx_t[v]);
            else W=e[i].w*len;
            if (W<ans) {ans=w;id=e[i].id;}
            else if (W==ans) id=min (id,e[i].id);
        DFS2 (V,u);
    }}} int main () {int t;scanf ("%d", &t);
        for (int g = 1; G <= T; g++) {scanf ("%d", &n);
        memset (head,-1,sizeof (head));
        cnt=0;
            for (int i = 1; i < n; i++) {int a,b,w;scanf ("%d%d%d", &a,&b,&w);
            Add_edge (A,b,w,i);
        Add_edge (B,a,w,i);
        } dis_s[1]=0;
        DFS (1,-1,dis_s);
        int S=1;
        for (int i = 1; I <= n; i++) if (dis_s[s]<dis_s[i]) s=i;
        dis_s[s]=0;
        DFS (s,-1,dis_s);
        LEN=DIS_S[1];
        int t=1;
        for (int i = 1; I <= n; i++) if (Dis_s[t]<dis_s[i]) {t=i;len=dis_s[t];}
        dis_t[t]=0;
        DFS (t,-1,dis_t);
        Get_max (t,-1,mx_s,dis_s); Get_max (s,-1,mx_t, dis_t);
        ANS=0X7FFFFFF;
        DFS2 (s,-1);
    printf ("Case #%d:%d\n", g,id);
} return 0; }