BZOJ3170 [Tjoi2013]松鼠聚会 切比雪夫距离 - 曼哈顿距离 - 前缀和

BZOJ3170

题意:


  有N个小松鼠,它们的家用一个点x,y表示,两个点的距离定义为:点(x,y)和它周围的8个点即上下左右四个点和对角的四个点,距离为1。现在N个松鼠要走到一个松鼠家去,求走过的最短距离。

n <= 1e5;

思路: 

  题意描述的是切比雪夫距离,就是两点之间的距离为max(dx,dy)。要求所有点的话,用曼哈顿距离配上前缀和能比较快得求出来。

  所以要把切比雪夫距离转化为曼哈顿距离。

  曼哈顿距离通过对x,y坐标分别排序求前缀和,可以O(n)得出所有点的曼哈顿距离前缀和。

#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 << "\n";
#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;
typedef pair<ll,int>pli;
//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 '\n'
//#define R register
#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----------------------*/

            const int maxn = 1e5+9;
            struct node
            {
                ll x,y;
                int id;
            }p[maxn];

            bool cmpx(node a, node b){
                return a.x < b.x;
            }

            bool cmpy(node a,node b){
                return a.y < b.y;
            }
            ll sum[maxn],sx[maxn],sy[maxn];
int main(){
            int n;  
            scanf("%d", &n);
            for(int i=1; i<=n; i++){
                ll x,y;
                scanf("%lld%lld", &x, &y);
                p[i].x = x+y;
                p[i].y = x-y;
                p[i].id = i;
            }

            sort(p+1,p+1+n,cmpx);

            for(int i=1; i<=n; i++) sx[i] = sx[i-1] + p[i].x;
            for(int i=1 ;i<=n; i++){

                sum[p[i].id] = p[i].x*(i-1) - sx[i-1] + sx[n] - sx[i] - p[i].x*(n-i);
            }

            sort(p+1,p+1+n,cmpy);

            for(int i=1; i<=n; i++) sy[i] = sy[i-1] + p[i].y;

            ll ans = inff;

            for(int i=1 ;i<=n; i++){

                ll tmp = p[i].y*(i-1) - sy[i-1] + sy[n] - sy[i] - p[i].y*(n-i);
                ans = min(ans, sum[p[i].id] + tmp);
            }
            printf("%lld\n", ans/2);
            return 0;   
}
View Code

猜你喜欢

转载自www.cnblogs.com/ckxkexing/p/10317560.html