Python recursion and global cache

  • 0
    cache = {}
    class Solution(object):
        def numTrees(self, n):
            def helper(n):
                if n in cache: return cache[n]
                res = sum([(helper(i) or 1) * (helper(n - i - 1) or 1) for i in xrange(n)])
                cache[n] = res
                return res
            return helper(n)

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