Submission #4573

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Source Code Expand

#include <iostream>
#include <vector>
#include <cmath>
using namespace std;

double get_r(pair<double,double> a, pair<double,double> b)
{
  return sqrt((a.first-b.first)*(a.first-b.first)+(a.second-b.second)*(a.second-b.second));
}

int main()
{
  int N;
  double start, goal;
  vector<pair<double, double>> course;
  cin >> N;
  cin >> start >> goal;
  for(int i=0;i<=N;++i)
  {
    double l,r;
    cin >> l >> r;
    course.push_back({l,r});
  }

  double result = 0.0;
  pair<double,double> begin = {start, 0};
  pair<double,double> end = {goal, N};
  for(int i=0;i<=N;++i)
  {
    double pos = begin.first + (begin.first - end.first)
      /(begin.second - end.second)
      *(static_cast<double>(i)-begin.second);
    if(pos>=course[i].first && pos<=course[i].second) continue;

    pair<double,double> tmp;
    if(pos<course[i].first) tmp = {course[i].first, i};
    if(pos>course[i].second) tmp = {course[i].second, i};
    result += get_r(begin, tmp);
    begin = tmp;
  }
  result += get_r(begin, end);

  printf("%.14f\n", result);
  return 0;
}

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