ZOJ 3278 8G Island 二分+二分

int n,m;
LL K;
LL a[maxn],b[maxn];
bool C(LL x){
    LL res=0;
    for (int i=1;i<=n;i++) {
        int l=1,r=m;
        LL ans=0;
        while (l<=r){
            int mid=(l+r)/2;
            if (1LL*a[i]*b[mid]>=x){
                ans=mid;
                l=mid+1;
            }
            else r=mid-1;
        }
        res+=ans;
    }
    return res>=K;
}
int main(){
    while (cin>>n>>m>>K){
        for (int i=1;i<=n;i++) cin>>a[i];
        for (int i=1;i<=m;i++) cin>>b[i];
        sort(a+1,a+n+1,greater<int>());
        sort(b+1,b+m+1,greater<int>());
        LL l=1LL*a
*b[m],r=1LL*a[1]*b[1];
        LL ans=l;
        while (l<=r) {
            LL mid=(l+r)/2;
            if (C(mid)) {
                ans=mid;
                l=mid+1;
            }
            else r=mid-1;
        }
        cout<<ans<<endl;
    }
	return 0;
}