【蓝桥-2017国赛】【二分】6.区间位移

#include<bits/stdc++.h>
using namespace std;
int n;


struct Node{
  int a;
  int b;
};

vector<Node> s;

bool ngreater(Node x, Node y){
  return x.b < y.b;
}

bool check(int mid){
  vector<Node> temp(s);
  int mr = 0;
  while(true){
    bool flag = false;
    for(int i = 0; i < temp.size(); i++){
      int x = temp[i].a;
      int y = temp[i].b;
      int len = y - x;

      if(x - mid <= mr && y + mid >= mr){
        flag = true;
        if(x + mid >= mr){
          mr += len;
        }
        else{
          mr = y + mid;
        }
        temp.erase(temp.begin() + i);
        break;
      }
    }
    if(mr >= 20000 || !flag) break;
  }
  return mr >= 20000;
}

int main()
{
  cin >> n;
  for(int i = 0; i < n; i++){
    int x, y;
    scanf("%d%d", &x, &y);
    s.push_back({x * 2, y * 2});
  }
  sort(s.begin(), s.end(), ngreater);
  int mid;
  int min;
  int left = 0, right = 20000;
  while(left <= right){
    mid = (left + right) >> 1;
    if(check(mid)){
      right = mid - 1;
      min = mid;
    }
    else{
      left = mid + 1;
    }
  }
  double res = ((double)min) / 2;
  cout << res;
}