[bzoj]4590: [Shoi2015]自動刷題機

二分答案，暴力驗證。找到一個最小滿足的值與一個最大滿足的值。

記得最後判斷二分的是否正確。

#include <cstdio>
#include <algorithm>
#define ll long long
using namespace std;
int n,k;
ll w[100005];
ll sum,x,y;
inline ll pd(ll x)
{
	register int i;
	ll now=0,ret=0;
	for (i=1;i<=n;i++)
	{
		now+=w[i];
		if (now<0) now=0;
		if (now>=x) ret++,now=0;
	}
	return ret;
}
inline ll efmi(ll l,ll r)
{
	ll mid,ret=0;
	while (l<=r)
	{
		mid=(l+r)>>1;
		if (pd(mid)<=k) r=mid-1,ret=mid;
		else l=mid+1;
	}
	return ret;
}
inline ll efma(ll l,ll r)
{
	ll mid,ret=0;
	while (l<=r)
	{
		mid=(l+r)>>1;
		if (pd(mid)>=k) l=mid+1,ret=mid;
		else r=mid-1;
	}
	return ret;
}
int main()
{
	register int i,j;
	scanf("%d %d",&n,&k);
	for (i=1;i<=n;i++)
	{
		scanf("%lld",&w[i]);
		sum+=abs(w[i]);
	}
	x=efmi(1,sum);y=efma(1,sum);
	if (pd(x)!=k||pd(y)!=k) printf("-1");
	else printf("%lld %lld",x,y);
	return 0;
}