Rubyならこんな感じ。
適当に関数型に変えてくれ。
def aaa(remain, target, ok)
p tmp = rand > 0.5
ok += 1 if tmp
return true if ok >= target
if remain + ok < target
return false
else
return aaa(remain - 1, target, ok)
end
end

remain = 10
target = 8
ok = 0

p ['result =', aaa(remain, target, ok)]