bzoj 1734: [Usaco2005 feb]Aggressive cows 愤怒的牛【二分+贪心】

二分答案，贪心判定

#include<iostream>
#include<cstdio>
#include<algorithm>
using namespace std;
const int N=100005;
int n,m,a[N];
int read()
{
    int r=0,f=1;
    char p=getchar();
    while(p>'9'||p<'0')
    {
        if(p=='-')
            f=-1;
        p=getchar();
    }
    while(p>='0'&&p<='9')
    {
        r=r*10+p-48;
        p=getchar();
    }
    return r*f;
}
bool ok(int w)
{
    int tot=1,pr=1,la=1;  
    while(tot<=m)  
    {  
        while(a[pr]-a[la]<w&&pr<=n) 
            pr++;  
        if(pr>n&&tot<m) 
            return 0;  
        tot++,la=pr; 
    }  
    return 1;  
}
int main()
{
    n=read(),m=read();
    for(int i=1;i<=n;i++)
        a[i]=read();
    sort(a+1,a+1+n);
    int l=1,r=1e9,ans=0;
    while(l<=r)
    {
        int mid=(l+r)>>1;
        if(ok(mid))
            l=mid+1,ans=mid;
        else
            r=mid-1;
    }
    printf("%d\n",ans);
    return 0;
}