POJ

POJ-1741

题意：

对于带权的一棵树，求树中距离不超过k的点的对数。

思路：

点分治的裸题。　将这棵树分成很多小的树，分治求解。

#include <algorithm>
#include  <iterator>
#include  <iostream>
#include   <cstring>
#include   <cstdlib>
#include   <iomanip>
#include    <bitset>
#include    <cctype>
#include    <cstdio>
#include    <string>
#include    <vector>
#include     <cmath>
#include     <queue>
#include      <list>
#include       <map>
#include       <set>
using namespace std;
//#pragma GCC optimize(3)
//#pragma comment(linker, "/STACK:102400000,102400000")  //c++
#define lson (l , mid , rt << 1)
#define rson (mid + 1 , r , rt << 1 | 1)
#define debug(x) cerr << #x << " = " << x << "
";
#define pb push_back
#define pq priority_queue



typedef long long ll;
typedef unsigned long long ull;

typedef pair<ll ,ll > pll;
typedef pair<int ,int > pii;
typedef pair<int,pii> p3;

//priority_queue<int> q;//这是一个大根堆q
//priority_queue<int,vector<int>,greater<int> >q;//这是一个小根堆q
#define fi first
#define se second
//#define endl '
'

#define OKC ios::sync_with_stdio(false);cin.tie(0)
#define FT(A,B,C) for(int A=B;A <= C;++A)  //用来压行
#define REP(i , j , k)  for(int i = j ; i <  k ; ++i)
//priority_queue<int ,vector<int>, greater<int> >que;

const ll mos = 0x7FFFFFFFLL;  //2147483647
const ll nmos = 0x80000000LL;  //-2147483648
const int inf = 0x3f3f3f3f;
const ll inff = 0x3f3f3f3f3f3f3f3fLL; //18
const int mod = 998244353;

const double PI=acos(-1.0);

// #define _DEBUG;         //*//
#ifdef _DEBUG
freopen("input", "r", stdin);
// freopen("output.txt", "w", stdout);
#endif
/*-----------------------showtime----------------------*/
            const int maxn = 1e5+9;
            int root = 0,S,mx;
            int n,k;
            int sz[maxn],f[maxn],dis[maxn],cnt;
            bool used[maxn];
            struct node
            {
                int to,w,nx;
            }e[maxn];
            int h[maxn],tot = 0;
            void add(int u,int v,int w){
                e[tot].to = v;
                e[tot].w = w;
                e[tot].nx = h[u];
                h[u] = tot++;
            }
            void getRoot(int u, int fa){
                sz[u] = 1,f[u] = 1;
                for(int i = h[u] ; ~i; i= e[i].nx){
                    int v = e[i].to;
                    if(used[v] || fa == v)continue;
                    getRoot(v,u);
                    sz[u] += sz[v];
                    f[u] = max(f[u] , sz[v]);
                }
                f[u] = max(f[u],S - sz[u]);
                if(f[u] < mx){root = u;mx = f[u];}
            }

            void getDis(int u,int fa,int D){
                for(int i=h[u] ; ~i; i=e[i].nx){
                    int v = e[i].to;
                    if(used[v]||v == fa)continue;
                    dis[++cnt] = D + e[i].w;
                    getDis(v,u,dis[cnt]);
                }
            }

            int getAns(int x,int D){
                dis[cnt = 1] = D;
                getDis(x,0,D);
                sort(dis+1,dis+1+cnt);
                int le = 1,ri =cnt,ans = 0;
                while(le <= ri){
                    if(dis[le] + dis[ri] <= k)ans += ri - le,le++;
                    else ri--;
                }
                return ans;
            }

            int Divide(int x){
                used[x] = true;
                ll ans = getAns(x,0);
                for(int i=h[x]; ~i; i= e[i].nx){
                    int v = e[i].to;
                    if(used[v])continue;
                    ans -= getAns(v,e[i].w);
                    mx = inf,S = sz[v];
                    getRoot(v,x);ans += Divide(root);
                }
                return ans;
            }
int main(){
            
            while(~scanf("%d%d", &n, &k) && n+k)
            {
                memset(h,-1,sizeof(h));
                memset(used,false,sizeof(used));
                tot = 0;
                for(int i=1; i<n; i++){
                    int u,v,c;
                    scanf("%d%d%d", &u, &v,&c);
                    add(u,v,c);
                    add(v,u,c);
                }
                S = n;mx = inf;
                getRoot(1,-1);
                printf("%d
",Divide(root));
            }
            return 0;
}

自己今天又写了一遍。

//点分治
//#pragma GCC optimize(3)
//#pragma comment(linker, "/STACK:102400000,102400000")  //c++
// #pragma GCC diagnostic error "-std=c++11"
// #pragma comment(linker, "/stack:200000000")
// #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
// #pragma GCC optimize("-fdelete-null-pointer-checks,inline-functions-called-once,-funsafe-loop-optimizations,-fexpensive-optimizations,-foptimize-sibling-calls,-ftree-switch-conversion,-finline-small-functions,inline-small-functions,-frerun-cse-after-loop,-fhoist-adjacent-loads,-findirect-inlining,-freorder-functions,no-stack-protector,-fpartial-inlining,-fsched-interblock,-fcse-follow-jumps,-fcse-skip-blocks,-falign-functions,-fstrict-overflow,-fstrict-aliasing,-fschedule-insns2,-ftree-tail-merge,inline-functions,-fschedule-insns,-freorder-blocks,-fwhole-program,-funroll-loops,-fthread-jumps,-fcrossjumping,-fcaller-saves,-fdevirtualize,-falign-labels,-falign-loops,-falign-jumps,unroll-loops,-fsched-spec,-ffast-math,Ofast,inline,-fgcse,-fgcse-lm,-fipa-sra,-ftree-pre,-ftree-vrp,-fpeephole2",3)

#include <algorithm>
#include  <iterator>
#include  <iostream>
#include   <cstring>
#include   <cstdlib>
#include   <iomanip>
#include    <bitset>
#include    <cctype>
#include    <cstdio>
#include    <string>
#include    <vector>
#include     <stack>
#include     <cmath>
#include     <queue>
#include      <list>
#include       <map>
#include       <set>
#include   <cassert>

using namespace std;
#define lson (l , mid , rt << 1)
#define rson (mid + 1 , r , rt << 1 | 1)
#define debug(x) cerr << #x << " = " << x << "
";
#define pb push_back
#define pq priority_queue



typedef long long ll;
typedef unsigned long long ull;
//typedef __int128 bll;
typedef pair<ll ,ll > pll;
typedef pair<int ,int > pii;
typedef pair<int,pii> p3;

//priority_queue<int> q;//这是一个大根堆q
//priority_queue<int,vector<int>,greater<int> >q;//这是一个小根堆q
#define fi first
#define se second
//#define endl '
'

#define OKC ios::sync_with_stdio(false);cin.tie(0)
#define FT(A,B,C) for(int A=B;A <= C;++A)  //用来压行
#define REP(i , j , k)  for(int i = j ; i <  k ; ++i)
#define max3(a,b,c) max(max(a,b), c);
#define min3(a,b,c) min(min(a,b), c);
//priority_queue<int ,vector<int>, greater<int> >que;

const ll mos = 0x7FFFFFFF;  //2147483647
const ll nmos = 0x80000000;  //-2147483648
const int inf = 0x3f3f3f3f;
const ll inff = 0x3f3f3f3f3f3f3f3f; //18
const int mod = 1e9+7;
const double esp = 1e-8;
const double PI=acos(-1.0);
const double PHI=0.61803399;    //黄金分割点
const double tPHI=0.38196601;


template<typename T>
inline T read(T&x){
    x=0;int f=0;char ch=getchar();
    while (ch<'0'||ch>'9') f|=(ch=='-'),ch=getchar();
    while (ch>='0'&&ch<='9') x=x*10+ch-'0',ch=getchar();
    return x=f?-x:x;
}


/*-----------------------showtime----------------------*/
/*
using namespace std;
#define pb push_back
#define debug(x) cerr<<#x<<" = " << x<<endl;
#define fi first
#define se second
typedef pair<int,int> pii;
const int inf = 0x3f3f3f3f;

*/
        int n,k,ans;
        const int maxn = 10009;
        vector<pii>mp[maxn];
        int dp[maxn],cen[maxn];
        void getsize(int u,int fa){
            dp[u] = 1;
            for(int i=0; i<mp[u].size(); i++){
                int v = mp[u][i].fi;
                if(fa == v || cen[v]) continue;
                getsize(v, u);
                dp[u] += dp[v];
            }
        }

        pii getbig(int u,int fa,int t){
            pii res = pii(inf, u);
            int mx = 0;
            for(int i=0; i<mp[u].size(); i++){
                int v = mp[u][i].fi;
                if(v == fa || cen[v])continue;
                res = min(res, getbig(v, u, t));
                mx = max(mx, dp[v]);
            }

            res = min(res, pii(max(mx, t - dp[u]), u));
            return res;
        }

        void dfs(int u,int fa,int c, vector<int> & b){
            b.pb(c);
            for(int i=0; i<mp[u].size(); i++){
                int v = mp[u][i].fi,d = c + mp[u][i].se;
                if(v == fa || cen[v])continue;
                dfs(v,u,d,b);
            }
        }
        int cal(vector<int>&b){

            sort(b.begin(), b.end());

            int res = 0,r = b.size();
            for(int i=0; i<b.size(); i++){
                while(r && b[i] + b[r-1] > k) r--;
                if(r > i) res += r - 1;
                else res += r;
            }
            return res/2;
        }

        void solve(int u){
            getsize(u, -1);
            int s = getbig(u, -1,dp[u]).se;
            cen[s] = 1;

            for(int i=0; i<mp[s].size(); i++){
                int v = mp[s][i].fi;
                if(cen[v])continue;
                solve(v);
            }

            vector<int>a;
            a.pb(0);
            for(int i=0; i<mp[s].size(); i++)
            {
                int v = mp[s][i].fi;
                if(cen[v])continue;

                vector<int>b;
                dfs(v, s, mp[s][i].se, b);
                ans -= cal(b);
                a.insert(a.end(),b.begin(),b.end());
            }

            ans += cal(a);
            cen[s] = 0;
        }
int main(){
        while(~scanf("%d%d", &n, &k) && n + k){
            for(int i=1; i<=n; i++) mp[i].clear();
            for(int i=1; i<n; i++){
                int u,v,w;
                scanf("%d%d%d", &u, &v, &w);
                mp[u].pb(pii(v,w));
                mp[v].pb(pii(u,w));
            }
            ans = 0;
            solve(1);
            printf("%d
", ans);
        }
        return 0;
}