The Latest Time to Catch a Bus

Solution.cs

public class Solution {
  public int LatestTimeCatchTheBus(int[] buses, int[] passengers, int capacity) {
    PriorityQueue<int, int> qbus = new();
    PriorityQueue<int, int> qpass = new();
    HashSet<int> set = new();
    
    foreach(var bus in buses) qbus.Enqueue(bus, bus);
    
    foreach(var p in passengers)
    {
      qpass.Enqueue(p, p);
      set.Add(p);
    }
    
    while(qbus.Count > 0)
    {
      int lbus = qbus.Dequeue();
      int c = capacity;
      int lastp = 0;
      while(c > 0)
      {
        if(qpass.Count > 0 && qpass.Peek() <= lbus)
        {
          lastp = qpass.Dequeue();
          c--;
        } else break;
      }
      // for the last bus
      if(qbus.Count == 0)
      {
        if(lastp == 0) return lbus;
        if(c > 0)
        {
          int res = 0;
          for(int i = lastp+1; i <= lbus; i++)
          {
            if(set.Contains(i)) continue;
            res = i;
          }
          if(res > 0) return res;
        }
        
        for(int i = lastp-1; i >= 0; i--)
        {
          if(set.Contains(i)) continue;
          return i;
        }
      }
    }
    
    return -1;
  }
}

/*

nlogn+nlogn+n

10 - 4
20 - 11,13
30 - { 19,21,25,26 }


10 - 2
20 - { 17, 18, 19 }

latest time's passengers -> capacity'th passenger -- untill there is a space

*/