AvoidObstacles.cs

static int avoidObstacles(int[] obs) 
    { 
        // Insert all array elements in a hash table 
        // and find the maximum value in the array 
        HashSet<int> hs = new HashSet<int>();  //HashSet contains no duplicate elements, and whose elements are in no particular order.
        int max = obs[0]; 
        for (int i = 0; i < obs.Length; i++)  
        { 
            hs.Add(obs[i]); 
            max = Math.Max(max, obs[i]); 
        } 
  
        // checking for every possible length which 
        // yield us solution 
        for (int i = 1; i <= max; i++)  
        { 
            int j; 
            for (j = i; j <= max; j = j + i) 
            { 
  
                // if there is obstacle, break the loop. 
                if (hs.Contains(j))  
                    break; 
            } 
  
            // If above loop did not break 
            if (j > max)  
                return i;          
        } 
        return max+1; 
    }