View difference between Paste ID: kQVK4h6E and g9ZBMKdZ

 n, s = gets.strip.split(' ')
 n = n.to_i
 s = s.to_i
 
 used_start_poins = Hash.new
 used_end_points = Hash.new
 
 for a0 in (0..s-1)
   l, r = gets.strip.split(' ')
   l = l.to_i
   r = r.to_i
 
   sum = 0
   if l > 0
     sum += r*(r+1)/2 - (l*(l-1)/2)
   else
     sum += r*(r+1)/2
   end
 
   used_start_poins[l]=r
   used_end_points[r]=l
 
   left = l-1
 
   while left > 0
     i = used_end_points[left]
 
     if i
       left = used_start_poins[i]-1
     else
       sum += left
       used_start_poins[l]=l
       used_end_points[l]=l
       break
     end
   end
 
   right = r+1
 
   while right < n
     i = used_start_poins[right]
 
     if i
       right = used_end_points[i]+1
     else
       sum += right
       used_start_poins[r]=r
       used_end_poins[r]=r