【BZOJ】3834: [Poi2014]Solar Panels

http://www.lydsy.com/JudgeOnline/problem.php?id=3834

题意：求$max{(i,j)}, smin<=i<=smax, wmin<=i<=wmax$，其中$smin<=smax<=10^9, wmin<=wmax<=10^9$，有$N<=1000$组数据

#include <bits/stdc++.h>
using namespace std;
int main() {
	int cs, smin, smax, wmin, wmax, ans; scanf("%d", &cs);
	while(cs--) {
		scanf("%d%d%d%d", &smin, &smax, &wmin, &wmax);
		if(smax>wmax) swap(smin, wmin), swap(smax, wmax);
		ans=1;
		if(wmin<=smax && smax<=wmax) ans=smax;
		else {
			--smin; --wmin;
			for(int d=smax, pos; d; d=pos) {
				pos=max(smax/(smax/d+1), wmax/(wmax/d+1));
				if(smin>=d) pos=max(pos, smin/(smin/d+1));
				if(wmin>=d) pos=max(pos, wmin/(wmin/d+1));
				if(smax/d-smin/d>0 && wmax/d-wmin/d>0) { ans=d; break; }
			}
		}
		printf("%d
", ans);
	}
	return 0;
}

　　

假设$smax<=wmax$

如果$wmin<=smax<=wmax$，显然答案就是$smax$

考虑枚举$d=gcd$，那么转换为在区间$[ lfloor frac{smin}{d} floor, lfloor frac{smax}{d} floor ] 和 [ lfloor frac{wmin}{d} floor, lfloor frac{wmax}{d} floor ]$找$[(i, j)]=1$表示存在$gcd(i,j)=d$

于是我就很sb了............我为什么一定要$[(i,j)]=1$呢.............然后膜拜了zyf千古神犇....发现其实$[(i,j)]>=1$就行了= =.............因为我很sb没想到.......倍数关系啊= =

于是分块查询即可..

复杂度$O(N4sqrt{smax})$