HDU 2295 Radar (DLX + 二分)

Radar

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 2882    Accepted Submission(s): 1113

Problem Description

N cities of the Java Kingdom need to be covered by radars for being in a state of war. Since the kingdom has M radar stations but only K operators, we can at most operate K radars. All radars have the same circular coverage with a radius of R. Our goal is to minimize R while covering the entire city with no more than K radars.

 

Input

The input consists of several test cases. The first line of the input consists of an integer T, indicating the number of test cases. The first line of each test case consists of 3 integers: N, M, K, representing the number of cities, the number of radar stations and the number of operators. Each of the following N lines consists of the coordinate of a city.
Each of the last M lines consists of the coordinate of a radar station.

All coordinates are separated by one space.
Technical Specification

1. 1 ≤ T ≤ 20
2. 1 ≤ N, M ≤ 50
3. 1 ≤ K ≤ M
4. 0 ≤ X, Y ≤ 1000

 

Output

For each test case, output the radius on a single line, rounded to six fractional digits.

 

Sample Input

1 3 3 2 3 4 3 1 5 4 1 1 2 2 3 3

 

Sample Output

2.236068

 

 

 

 

昨天用G++交T了一下午，刚才换C++交了一发报RE了，发现是数组开小了，改后重交就过了，早知道是RE昨天就不会那么头疼了，再也不信G++。

用二分来找答案，城市作为列，每个雷达最为行，行和列的组合就是此雷达能否覆盖这个城市，每次给出一个二分数值后构造一个矩阵，然后dancing一下，如果能得到答案那么将值减小再尝试，反之加大。

#include <iostream>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#include <cstdlib>
#include <cmath>
#include <cstdio>
using    namespace    std;

struct    Node
{
    double    x,y;
};

const    int    HEAD = 0;
const    int    SIZE = 55;
int    N,M,K;
double    RADAR[SIZE][SIZE];
Node    CITY[SIZE];
bool    VIS[SIZE];
int    U[SIZE * SIZE],D[SIZE * SIZE],L[SIZE * SIZE],R[SIZE * SIZE],C[SIZE * SIZE],S[SIZE * SIZE];

int    comp(const void * a,const void * b);
int    h(void);
void    debug(int count);
void    ini(void);
bool    dancing(int);
void    remove(int);
void    resume(int);

int    main(void)
{
    int    t;
    double    x,y;

    scanf("%d",&t);
    while(t --)
    {
        scanf("%d%d%d",&N,&M,&K);
        for(int i = 0;i < N;i ++)
            scanf("%lf%lf",&CITY[i].x,&CITY[i].y);
        for(int i = 0;i < M;i ++)
        {
            scanf("%lf%lf",&x,&y);
            for(int j = 0;j < N;j ++)
                RADAR[i][j] = sqrt(pow(CITY[j].x - x,2) + pow(CITY[j].y - y,2));
        }

        double    l = 0,r = 1500;
        double    mid = 0;
        while(r - l > 1e-7)
        {
            mid = (l + r) / 2;
            ini();

            int    count = N + 1;
            for(int i = 0;i < M;i ++)
            {
                int    first = count;
                for(int j = 0;j < N;j ++)
                    if(RADAR[i][j] <= mid)
                    {
                        R[count] = count + 1;
                        L[count] = count - 1;
                        U[count] = U[j + 1];
                        D[count] = j + 1;

                        D[U[j + 1]] = count;
                        U[j + 1] = count;

                        C[count] = j + 1;
                        S[j + 1] ++;
                        count ++;
                    }
                L[first] = count - 1;
                if(first != count)
                    R[count - 1] = first;
            }
            //debug(count );
            if(dancing(0))
                r = mid;
            else    
                l = mid;
        }

        printf("%lf
",mid);
    }

    return    0;
}

void    ini(void)
{
    R[HEAD] = 1;
    L[HEAD] = N;
    for(int i = 1;i <= N;i ++)
    {
        L[i] = i - 1;
        R[i] = i + 1;
        U[i] = D[i] = C[i] = i;
        S[i] = 0;
    }
    R[N] = HEAD;
}

bool    dancing(int k)
{
    if(R[HEAD] == HEAD)
        return    true;
    if(k + h() > K)
        return    false;

    int    c = R[HEAD];
    for(int i = R[HEAD];i != HEAD;i = R[i])
        if(S[c] > S[i])
            c = i;

    for(int i = D[c];i != c;i = D[i])
    {
        remove(i);
        for(int j = R[i];j != i;j = R[j])
            remove(j);
        if(dancing(k + 1))
            return    true;
        for(int j = L[i];j != i;j = L[j])
            resume(j);
        resume(i);
    }

    return    false;
}

void    remove(int c)
{
    for(int i = D[c];i != c;i = D[i])
    {
        L[R[i]] = L[i];
        R[L[i]] = R[i];
    }
}

void    resume(int c)
{
    for(int i = D[c];i != c;i = D[i])
    {
        L[R[i]] = i;
        R[L[i]] = i;
    }
}

void    debug(int count)
{
    for(int i = 0;i < count;i ++)
        printf("%d U:%d D:%d L:%d R:%d C:%d S:%d
",i,U[i],D[i],L[i],R[i],C[i],S[i]);
    cout << endl << endl;
}

int    h(void)
{
    fill(VIS,VIS + SIZE,false);
    
    int    count = 0;
    for(int i = R[HEAD];i;i = R[i])
        if(!VIS[i])
        {
            count ++;
            VIS[i] = true;
            for(int j = D[i];j != i;j = D[j])
                for(int k = R[j];k != j;k = R[k])
                    VIS[C[k]] = true;
        }
    return    count;
}