<p>Given an integer array <code>nums</code>, return <em>the sum of divisors of the integers in that array that have exactly four divisors</em>. If there is no such integer in the array, return <code>0</code>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> nums = [21,4,7]
<strong>Output:</strong> 32
<strong>Explanation:</strong> 
21 has 4 divisors: 1, 3, 7, 21
4 has 3 divisors: 1, 2, 4
7 has 2 divisors: 1, 7
The answer is the sum of divisors of 21 only.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> nums = [21,21]
<strong>Output:</strong> 64
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> nums = [1,2,3,4,5]
<strong>Output:</strong> 0
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= nums.length &lt;= 10<sup>4</sup></code></li>
	<li><code>1 &lt;= nums[i] &lt;= 10<sup>5</sup></code></li>
</ul>

class Solution {
public:
public:
    int sumFourDivisors(const vector<int>& nums) {
        int ret = 0;
        std::unordered_map<int,int> numToDivSum;

        for (int x : nums)
        {
            if (!numToDivSum.contains(x))
                numToDivSum[x] = calcDivisorSum(x);
            ret += numToDivSum[x];
        }

        return ret;
    }
private:
    int calcDivisorSum(int x) const noexcept {
        std::unordered_set<int> divisors{1,x};
        for (int i=2; i <= sqrt(x) && divisors.size() <= 4; ++i)
        {
            if ((x % i) == 0)
            {
                divisors.insert(i);
                divisors.insert(x/i);
            }
        }
        return (divisors.size() == 4 ? std::accumulate(divisors.begin(), divisors.end(), 0) : 0);
    }
};
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