poj3241

曼哈顿最小树。

#include<iostream>
#include<cstring>
#include<algorithm>
#include<cmath>
#include<cstdlib>
#include<climits>
#include<stack>
#include<vector>
#include<queue>
#include<set>
#include<bitset>
#include<map>
//#include<regex>
#include<cstdio>
#pragma GCC optimize(2)
#define up(i,a,b)  for(int i=a;i<b;i++)
#define dw(i,a,b)  for(int i=a;i>b;i--)
#define upd(i,a,b) for(int i=a;i<=b;i++)
#define dwd(i,a,b) for(int i=a;i>=b;i--)
//#define local
typedef long long ll;
typedef unsigned long long ull;
const double esp = 1e-6;
const double pi = acos(-1.0);
const int INF = 0x3f3f3f3f;
const int inf = 1e9;
using namespace std;
ll read()
{
    char ch = getchar(); ll x = 0, f = 1;
    while (ch<'0' || ch>'9') { if (ch == '-')f = -1; ch = getchar(); }
    while (ch >= '0' && ch <= '9') { x = x * 10 + ch - '0'; ch = getchar(); }
    return x * f;
}
typedef pair<int, int> pir;
#define lson l,mid,root<<1
#define rson mid+1,r,root<<1|1
#define lrt root<<1
#define rrt root<<1|1
const int N = 10010;
struct eg {
    int u, v, wi;
    bool operator<(const eg a) {
        return wi < a.wi;
    }
}edge[5 * N];
int eg_cnt = 0;
void addedge(int u, int v, int wi)
{
    edge[eg_cnt].u = u; edge[eg_cnt].v = v; edge[eg_cnt].wi = wi; eg_cnt++;
}
struct uni {
    int height[N], fa[N];
    void init(int maxn)
    {
        upd(i, 0, maxn)
        {
            height[i] = 1;
            fa[i] = i;
        }
    }
    int find_pr(int x)
    {
        return x == fa[x] ? x : fa[x] = find_pr(fa[x]);
    }
    void unit(int x, int y)
    {
        x = find_pr(x);
        y = find_pr(y);
        if (x == y)return;
        if (height[x] < height[y])swap(x, y);
        fa[y] = x;
        height[x] += height[y];
    }
    bool same(int x, int y)
    {
        return find_pr(x) == find_pr(y);
    }
}un;
struct dij{
    int a, b, id;
    bool operator<(const dij tp)const
    {
        return a == tp.a ? b < tp.b : a < tp.a;
    }
}now[N];
struct bit {
    int minn[N];
    int id[N];
    int len;
    void init(int len)
    {
        this->len = len;
        memset(bit::minn, INF, sizeof(bit::minn));
        memset(bit::id, 0, sizeof(bit::id));
    }
    int lowbit(int i)
    {
        return i & (-i);
    }
    void update(int pos, int val,int id)
    {
        while (pos)
        {
            if (minn[pos] > val)
            {
                bit::minn[pos] = val;
                bit::id[pos] = id;
            }
            pos -= bit::lowbit(pos);
        }
    }
    int query(int pos)
    {
        int temp_min = INF;
        int temp_pos = 0;
        while (pos <= len)
        {
            if (temp_min > minn[pos])
            {
                temp_min = minn[pos];
                temp_pos = id[pos];
            }
            pos += bit::lowbit(pos);
        }
        return temp_pos;
    }
}BIT;
int n, k;
vector<int>vec;
int distemp[N];
int dist(int x, int y)
{
    return abs(now[x].b - now[y].b) + abs(now[x].a - now[y].a);
}
void cal()
{
    upd(i, 1, n)
    {
        distemp[i] = now[i].b - now[i].a;
        vec.push_back(distemp[i]);
    }
    sort(vec.begin(), vec.end());
    vec.erase(unique(vec.begin(), vec.end()), vec.end());
    BIT.init(vec.size());
    dwd(i, n, 1)
    {
        int cal_pos = lower_bound(vec.begin(), vec.end(), distemp[i]) - vec.begin() + 1;
        int f_pos = BIT.query(cal_pos);
        if (f_pos != 0)
            addedge(now[i].id, now[f_pos].id, dist(i, f_pos));
        BIT.update(cal_pos, now[i].a + now[i].b, i);
    }
}
void kruskal()
{
    k = n - k;
    int kru_tot = 0;
    sort(edge, edge + eg_cnt);
    vector<int>ans;
    up(i, 0, eg_cnt)
    {
        if (!un.same(edge[i].u, edge[i].v))
        {
            kru_tot++;
            un.unit(edge[i].u, edge[i].v);
            if (kru_tot == k) { printf("%d\n", edge[i].wi); return; }
            //ans.push_back(edge[i].wi);
        }
    }
    //for (auto p : ans)printf("%d ", p);
    //printf("%d\n", ans[n - k]);
}
int main()
{
    n = read(), k = read();
    un.init(n);
    upd(i, 1, n)
    {
        now[i].a = read(); now[i].b = read(); now[i].id = i;
    }
    up(j, 0, 4)
    {
        if (j == 1||j==3)
        {
            upd(i, 1, n)swap(now[i].a, now[i].b);
        }
        else if (j == 2)
        {
            upd(i, 1, n)now[i].a = -now[i].a;
        }
        sort(now + 1, now + n + 1);
        cal();
    }
    kruskal();
    return 0;
}

poj3241

原文：https://www.cnblogs.com/LORDXX/p/12506415.html