暑假集训Day13 C (二分+贪心)

题目链接在这里：Problem - C - Codeforces

网上很多说要用hall定理，emm还不太会用，不过这题可以贪心解决

就是feasible里面，每个男的只要选范围内离自己最远的那个女的就行

这里的贪心策略还是值得学习的

#include "bits/stdc++.h"
using namespace std;
typedef long long LL;
const LL MAX=1e6+5;
LL n,l,a[MAX],b[MAX],c[MAX];
LL fa[MAX];
bool vis[MAX];
bool feasible(LL x){
    LL i,j,k,an=0,low,high;
    j=1,k=c[0];
    for (i=1;i<=n;i++,j++,k++){
        for (;j<=k && abs(a[i]-c[j])>x;j++);
        for (;j<=k && abs(a[i]-c[k])>x;k--);
    }
    if (k<j) return false;
    return true;
}
int main(){
    LL i,j;
    scanf("%lld%lld",&n,&l);c[0]=0;
    for (i=1;i<=n;i++) scanf("%lld",a+i);
    for (i=1;i<=n;i++) scanf("%lld",b+i),c[++c[0]]=b[i];
    sort(a+1,a+n+1),sort(b+1,b+n+1);
    for (i=1;i<=n;i++) c[++c[0]]=b[i]-l,c[++c[0]]=b[i]+l;

    sort(c+1,c+c[0]+1);
    LL low,high,mid,ans;
    low=0,high=l;
    while (low<=high){
        mid=(low+high)>>1;
        if (feasible(mid)){
            ans=mid;
            high=mid-1;
        }
        else
            low=mid+1;
    }
    printf("%lld",ans);
    return 0;
}