POJ 1741（树分治）

﹏ヽ暗。殇╰゛Y 2022-08-05 00:57 149阅读 0赞

树分治第一题

论文题：

树的点分治

//      whn6325689
    //		Mr.Phoebe
    //		http://blog.csdn.net/u013007900
    #include <algorithm>
    #include <iostream>
    #include <iomanip>
    #include <cstring>
    #include <climits>
    #include <complex>
    #include <fstream>
    #include <cassert>
    #include <cstdio>
    #include <bitset>
    #include <vector>
    #include <deque>
    #include <queue>
    #include <stack>
    #include <ctime>
    #include <set>
    #include <map>
    #include <cmath>
    #include <functional>
    #include <numeric>
    #pragma comment(linker, "/STACK:1024000000,1024000000")
    
    
    using namespace std;
    
    typedef long long ll;
    typedef long double ld;
    typedef pair<ll, ll> pll;
    typedef complex<ld> point;
    typedef pair<int, int> pii;
    typedef pair<pii, int> piii;
    typedef vector<int> vi;
    
    #define CLR(x,y) memset(x,y,sizeof(x))
    #define mp(x,y) make_pair(x,y)
    #define pb(x) push_back(x)
    #define lowbit(x) (x&(-x))
    #define MID(x,y) (x+((y-x)>>1))
    #define speed std::ios::sync_with_stdio(false);
    #define eps 1e-9
    #define PI acos(-1.0)
    #define INF 0x3f3f3f3f
    #define LLINF 1LL<<62
    
    template<class T>
    inline bool read(T &n)
    {
        T x = 0, tmp = 1;
        char c = getchar();
        while((c < '0' || c > '9') && c != '-' && c != EOF) c = getchar();
        if(c == EOF) return false;
        if(c == '-') c = getchar(), tmp = -1;
        while(c >= '0' && c <= '9') x *= 10, x += (c - '0'),c = getchar();
        n = x*tmp;
        return true;
    }
    template <class T>
    inline void write(T n)
    {
        if(n < 0)
        {
            putchar('-');
            n = -n;
        }
        int len = 0,data[20];
        while(n)
        {
            data[len++] = n%10;
            n /= 10;
        }
        if(!len) data[len++] = 0;
        while(len--) putchar(data[len]+48);
    }
    //-----------------------------------
    
    const int MAXN=10010;
    
    struct Edge
    {
    	int v,nex,w;
    } e[MAXN<<1];
    int h[MAXN],tot;
    int vis[MAXN],n,k;
    
    int sz[MAXN],num[MAXN],dep[MAXN];
    int root,N;
    int st[MAXN],top,ans;
    
    void init()
    {
    	CLR(h,-1);CLR(vis,0);
    	root=0;num[0]=N=n;ans=0;tot=0;
    }
    
    void addedge(int u,int v,int w)
    {
    	e[tot].v=v;
    	e[tot].w=w;
    	e[tot].nex=h[u];
    	h[u]=tot++;
    }
    
    int dfs_root(int u,int fa=-1)
    {
    	sz[u]=1;num[u]=0;
    	for(int i=h[u];~i;i=e[i].nex)
    	{
    		int v=e[i].v;
    		if(fa==v || vis[v])	continue;
    		sz[u]+=dfs_root(v,u);
    		num[u]=max(num[u],sz[v]);
    	}
    	num[u]=max(num[u],N-sz[u]);
    	if(num[u]<num[root])
    		root=u;
    	return sz[u];
    }
    
    int dfs_dep(int u,int fa=-1)
    {
    	if(dep[u]<=k)	st[top++]=dep[u];
    	sz[u]=1;
    	for(int i=h[u];~i;i=e[i].nex)
    	{
    		int v=e[i].v;
    		if(fa==v || vis[v])	continue;
    		dep[v]=dep[u]+e[i].w;
    		sz[u]+=dfs_dep(v,u);;
    	}
    	return sz[u];
    }
    
    
    int get_num(int u,int len)
    {
    	top=0;
    	dep[u]=len;
    	dfs_dep(u);
    	sort(st,st+top);
    	int ans=0,r=top-1;
    	for(int l=0;l<r;l++)
    	{
    		while(r>l && st[l]+st[r]>k)
    			r--;
    		ans+=r-l;
    	}
    	return ans;
    }
    
    void dfs(int u)
    {
    	vis[u]=1;
    	ans+=get_num(u,0);
    	for(int i=h[u];~i;i=e[i].nex)
    	{
    		int v=e[i].v;
    		if(vis[v])	continue;
    		ans-=get_num(v,e[i].w);
    		root=0;N=sz[v];
    		dfs_root(v);
    		dfs(root);
    	}
    }
    
    int main()
    {
    	while(read(n)&&read(k)&&(n+k))
    	{
    		init();
    		for(int i=1,u,v,w;i<n;i++)
    		{
    			read(u),read(v),read(w);
    			addedge(u,v,w);addedge(v,u,w);
    		}
    		dfs_root(1);
    		dfs(root);
    		write(ans),putchar('\n');
    	}
    	return 0;
    }