Codeforces 782B The Meeting Place Cannot Be Changed(二分答案)

题目链接 The Meeting Place Cannot Be Changed

二分答案即可。

check的时候先算出每个点可到达的范围的区间，然后求并集。判断一下是否满足l <= r就好了。

eps我设了1e-7。

 #include <bits/stdc++.h>

 using namespace std;

 #define rep(i, a, b)              for(int i(a); i <= (b); ++i)

 const int N      =          +       ;
 const double eps =    1e-;

 double mi, ma;

 struct node{
     double x, y;
     friend bool operator < (const node &a, const node &b){
         return a.x < b.x;
     }
 }a[N];
 int n;

 double c[N], d[N];

 bool check(double x){
     rep(i, , n){
         c[i] = a[i].x - a[i].y * x;
         d[i] = a[i].x + a[i].y * x;
     }

     double l = c[], r = d[];
     rep(i, , n){
         l = max(l, c[i]);
         r = min(r, d[i]);
     }

     return l <= r;
 }

 int main(){

     mi = 2e9, ma = -mi;
     scanf("%d", &n);
     rep(i, , n){
         scanf("%lf", &a[i].x);
         mi = min(mi, a[i].x);
         ma = max(ma, a[i].x);
     }

     rep(i, , n){
         scanf("%lf", &a[i].y);
     }

     sort(a + , a + n + );

     double l = , r = ;
     while (abs(l - r) > eps){

         double mid = (l + r) / ;

         if (check(mid)) r = mid; else l = mid;
     }

     printf("%.10f\n", l);
     return ;

 }