343C - Read Time - CodeForces Solution

#include <iostream> 
#include <array> 

using namespace std;
using ll = long long;

int n, m;
array<ll, 100'000> h, p;

void input();

bool test(ll t){
  int i, j, k;
  for(i=0, j=0; i<n; ++i){
    ll a = abs(h[i] - p[j]);
    if(a > t){
      if(p[j] < h[i] || i == n-1)
          return false;
      else
        continue;
    }
    for(k = j+1; k < m; ++k){
      if(p[k] <= h[i]) continue;
      ll b = p[k] - h[i], c;
      if(p[j] < h[i])
        c = min(a+a+b, a+b+b);
      else
        c = max(a, b);
      if(c > t)
        break;
    }
    if(k == m) break;
    j = k;
  }

  return (i < n);
}

int main(){
  input();

  ll l = 0, r = 1e12;

  while(l < r){
    ll m = (r+l)/2;
    if(test(m))
      r = m;
    else
      l = m+1;
  }

  cout << l << '\n';

  return 0;
}

void input(){
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);

  cin >> n >> m;

  for(int i = 0; i < n; ++i)
    cin >> h[i];
  for(int i = 0; i < m; ++i)
    cin >> p[i];
}