Water collected between towers: Difference between revisions

=={{header|Scheme}}==

<lang scheme>

(import (scheme base)

(scheme write))

(define (total-collected chart)

(define (highest-right vals)

(if (null? (cdr vals))

'(0)

(cons (apply max (cdr vals))

(highest-right (cdr vals)))))

(define (highest-left vals)

(reverse (highest-right (reverse vals))))

;

(if (< (length chart) 3) ; catch the end cases

0

(apply +

(map (lambda (l c r)

(if (or (<= l c)

(<= r c))

0

(- (min l r) c)))

(highest-left chart)

chart

(highest-right chart)))))

(for-each

(lambda (chart)

(display chart) (display " -> ") (display (total-collected chart)) (newline))

'((1 5 3 7 2)

(5 3 7 2 6 4 5 9 1 2)

(2 6 3 5 2 8 1 4 2 2 5 3 5 7 4 1)

(5 5 5 5)

(5 6 7 8)

(8 7 7 6)

(6 7 10 7 6)))

</lang>

{{out}}

<pre>

(1 5 3 7 2) -> 2

(5 3 7 2 6 4 5 9 1 2) -> 14

(2 6 3 5 2 8 1 4 2 2 5 3 5 7 4 1) -> 35

(5 5 5 5) -> 0

(5 6 7 8) -> 0

(8 7 7 6) -> 0

(6 7 10 7 6) -> 0

(3 1 2) -> 1

(1) -> 0

() -> 0

(1 2) -> 0

</pre>