Towers of Hanoi: Difference between revisions
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}
</lang>
=={{header|Groovy}}==
Unlike most solutions here this solution manipulates more-or-less actual stacks of more-or-less actual rings.
<lang groovy>def tail = { list, n -> def m = list.size(); list[([m - n, 0].max())..<m] }
final STACK = [A:[],B:[],C:[]].asImmutable()
def report = { it -> }
def check = { it -> }
def moveRing = { from, to -> to << from.pop(); report(); check(to) }
def moveStack
moveStack = { from, to, using = STACK.values().find { !(it.is(from) || it.is(to)) } ->
if (!from) return
def n = from.size()
moveStack(tail(from, n-1), using, to)
moveRing(from, to)
moveStack(tail(using, n-1), to, from)
}</lang>
Test program:
<lang groovy>enum Ring {
S('°'), M('o'), L('O'), XL('()');
private sym
private Ring(sym) { this.sym=sym }
String toString() { sym }
}
report = { STACK.keySet().each { println "${it}: ${STACK[it]}" }; println() }
check = { to -> assert to == ([] + to).sort().reverse() }
Ring.values().reverseEach { STACK.A << it }
report()
check(STACK.A)
moveStack(STACK.A, STACK.C)</lang>
=={{header|Haskell}}==
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