fun higher_or_max(vs, v) =
 	let fun iterate(vs, max) = 
		case vs of
			[] => max
			| h::t => if h >= v then h else iterate(t, Int.max(max, h))
	in
		iterate(tl vs, hd vs)
	end
 
fun compute lst = 
	let fun sum(vs, height, v) = 
		case vs of 
			[] => 0
			| h::t => if h=v 
						then find_pit(h::t) 
						else (Int.min(height, v)-h) + sum(t, height, v)
	and
	find_pit(vs) = 
		case vs of
			h::n::t => if h>n 
						then sum(n::t, h, higher_or_max(n::t, h))
						else find_pit(n::t)
			| _ => 0
	in
		find_pit lst
	end
 
 
val t1 = [2,5,1,2,3,4,7,7,6]
val t2 = [0,5,0,1,0,2,1,0]
val t3 = [0,0,5,0,4,0,4,0,3]
val t4 = [0,0,5,0,100,0,4,0,3]
val t5 = [0,0,5,0,7,0,10,10,10]
val t6 = [0,0,7,0,3,0,5,0,2]
 
val c1 = compute(t1) = 10
val c2 = compute(t2) = 5
val c3 = compute(t3) = 11
val c4 = compute(t4) = 5+4+3
val c5 = compute(t5) = 12
val c6 = compute(t6) = 14
 

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