codeforces#242B-Megacity-二分

http://codeforces.com/problemset/problem/424/B

给n,s

给n个城市，以及里面人口

坐标中心0，0 有s人，

现在扩宽以0，0为中心，半径为r 圈一个圈，使得圈内人口大于等于1e6，求最小的r

直接二分R，每次判断够不够1e6

#include <cstdio>
#include <cmath>
#include <cstring>
#include <string>
#include <algorithm>
#include <queue>
#include <map>
#include <set>
#include <vector>
#include <iostream>
using namespace std;const double pi=acos(-1.0);
double eps=0.000001;
__int64 min(__int64 a,__int64 b)
{return a<b?a:b;}
__int64 max(__int64 a,__int64 b)
{return a>b?a:b;} __int64 n;
struct node
{__int64 x,y,z;double dis;
};
node tm[1005];
__int64 need=0;
__int64 bin(double x)
{__int64 sum=0;__int64 i;for (i=1;i<=n;i++){if (tm[i].dis<=x)sum+=tm[i].z;elsebreak;if (sum>=need) return 1;}return 0;
}
bool cmp(node a,node b)
{return a.dis<b.dis;}
int main()
{__int64 i,j;__int64 s;scanf("%I64d%I64d",&n,&s);for (i=1;i<=n;i++){scanf("%I64d%I64d%I64d",&tm[i].x,&tm[i].y ,&tm[i].z);tm[i].dis=tm[i].x*tm[i].x+tm[i].y*tm[i].y;}sort(tm+1,tm+1+n,cmp);need=1000000-s;double l=0;double r=1e10;double ans=-1;while(fabs(r-l)>eps){double mid=(l+r)/2;if (bin(mid))r=mid,ans=mid;elsel=mid;}if (ans==-1) printf("-1\n");elseprintf("%.6lf\n",sqrt(ans));return 0;}

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