Binary Trees With Factors.java

class Solution {
    int mod = 1000000007;
    HashMap<Integer, Long> dp;
    HashSet<Integer> set;
    
    public int numFactoredBinaryTrees(int[] arr) {
        long ans = 0;
        dp = new HashMap<>();
        set = new HashSet<>();
        
        for(int val : arr) set.add(val);
        
        for(int val : arr) {
			//giving each unique value a chance to be root node of the tree
            ans += solve(val, arr);
            ans %= mod;
        }
        
        return (int)ans;
    }
    
    public long solve(int val, int[] nums) {
        
        if(dp.containsKey(val)) {
            return dp.get(val);
        }
        
        long ans = 1;
        
        for(int i = 0; i < nums.length; i++) {
            if(val % nums[i] == 0 && set.contains(val / nums[i])) {
                long left = solve(nums[i], nums);
                long right = solve(val / nums[i], nums);
                
                ans += ((left * right) % mod);
                ans %= mod;
            }
        }
        
        dp.put(val, ans);
        
        return ans;
    }
}