LightOj1383 - Underwater Snipers（贪心 + 二分）

#include<stdio.h>
#include<iostream>
#include<string.h>
#include<algorithm>
#include<cmath>
#include<vector>
#include<queue>
#include<set>
using namespace std;
#define met(a, b) memset(a, b, sizeof(a))
#define maxn 10005
#define maxm 20005
#define INF 0x3f3f3f3f
typedef long long LL;

struct node
{
    int x, y;
    double L, R;
}a[maxn], b[maxn];

int n, s, k, D;

int cmp(node p, node q)
{
    if(p.R != q.R)
        return p.R < q.R;
    return p.L < q.L;
}

bool Judge(int d)
{
    for(int i=1; i<=n; i++)
    {
        if(a[i].y + d > D)
            return false;
    }
    met(b, 0);
    for(int i=1; i<=n; i++)
    {
        double y = a[i].y + d*1.0;
        double x = sqrt(1.0*D*D - y*y);
        b[i].L = a[i].x - x;
        b[i].R = a[i].x + x;
    }
    sort(b+1, b+n+1, cmp);
    int ans = 1;
    double R = b[1].R;
    for(int i=2; i<=n; i++)
    {
        if(b[i].L > R)
        {
            ans ++;
            R = b[i].R;
        }
    }
    return ans <= s;
}

int main()
{
    int T, t = 1;
    scanf("%d", &T);
    while(T--)
    {
        scanf("%d %d %d %d", &k, &n, &s, &D);
        for(int i=1; i<=n; i++)
        {
            scanf("%d %d", &a[i].x, &a[i].y);
            a[i].y -= k;
        }
        int L = 1, R = D, ans = -1;
        while(L <= R)
        {
            int Mid = (L+R)/2;
            if(Judge(Mid))
            {
                ans = Mid;
                L = Mid + 1;
            }
            else
                R = Mid - 1;
        }
        printf("Case %d: ", t++);
        if(ans == -1)
            puts("impossible");
        else
            printf("%d\n", ans);
    }
    return 0;
}