problem0823

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823. Binary Trees With Factors

题目

Given an array of unique integers, each integer is strictly greater than 1.

We make a binary tree using these integersand each number may be used for any number of times.

Each non-leaf node'svalue should be equal to the product of the values of it's children.

How many binary trees can we make? Return the answer modulo 10 ** 9 + 7.

Example 1:

Input: A = [2, 4]
Output: 3
Explanation: We can make these trees: [2], [4], [4, 2, 2]

Example 2:

Input: A = [2, 4, 5, 10]
Output: 7
Explanation: We can make these trees: [2], [4], [5], [10], [4, 2, 2], [10, 2, 5], [10, 5, 2].

Note:

1. 1 <= A.length <=1000.
2. 2 <=A[i]<=10 ^ 9.

解题思路

见程序注释