LeetCode题解(0823)：带因子的二叉树(Python)

题目：​​原题链接​​（中等）

标签：动态规划、树

解法一：

class Solution:
    _MOD = 10 ** 9 + 7

    def numFactoredBinaryTrees(self, A: List[int]) -> int:
        size = len(A)
        A.sort()

        count = {n: i for i, n in enumerate(A)}

        dp = [1] * size
        for i in range(size):
            v = A[i] * A[i]
            if v in count:
                k = count[v]
                dp[k] += dp[i] * dp[i]
            for j in range(i):
                v = A[i] * A[j]
                if v in count:
                    k = count[v]
                    dp[k] += dp[i] * dp[j] * 2
        return sum(dp) % self._MOD