UVA Watering Grass

贪心算法。

#include <iostream>
#include <cstdio>
#include <cstring>
#include <queue>
#include <cmath>
#include <vector>
#include <algorithm>
using namespace std;
#define lowbit(x) (x&(-x))
#define max(x,y) (x>y?x:y)
#define min(x,y) (x<y?x:y)
#define mem(a) (memset(a,0,sizeof(a)))
typedef long long ll;
struct Node
{
    double lx;
    double rx;
}node[10006];
bool cmp(Node a,Node b)
{
    return a.lx<b.lx;
}
int main()
{
    double n,m,w,l,r;
    while(scanf("%lf%lf%lf",&n,&m,&w)!=EOF)
    {
        int x=0,i,j,ans=0,ok=0;
        for(int i=0;i<n;i++)
        {
            scanf("%lf%lf",&l,&r);
            if(w/2>=r) continue;
            double t=(double)sqrt(r*r-((w*w)/4.0));
            node[x].lx=l-t;
            node[x].rx=l+t;
            x++;
        }
        sort(node,node+x,cmp);
        double left=0.0,right=0.0;
        if(node[0].lx<=0)
        {
            i=0;
            while(i<x)
            {
                j=i;
                while(j<x && node[j].lx<=left)
                {
                    if(node[j].rx>right)
                    {
                        right=node[j].rx;
                    }
                    j++;
                }
                if(i==j) break;
                i=j;
                ans++;
                left=right;
                if(left>=m)
                {
                    ok=1;
                    break;
                }
            }
        }
        if(ok)printf("%d\n",ans);
        else printf("-1\n");
    }
    return 0;
}