<p>Given an integer array <code>nums</code>, return <code>true</code> <em>if you can partition the array into two subsets such that the sum of the elements in both subsets is equal or </em><code>false</code><em> otherwise</em>.</p>

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

<pre>
<strong>Input:</strong> nums = [1,5,11,5]
<strong>Output:</strong> true
<strong>Explanation:</strong> The array can be partitioned as [1, 5, 5] and [11].
</pre>

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

<pre>
<strong>Input:</strong> nums = [1,2,3,5]
<strong>Output:</strong> false
<strong>Explanation:</strong> The array cannot be partitioned into equal sum subsets.
</pre>

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

<ul>
	<li><code>1 &lt;= nums.length &lt;= 200</code></li>
	<li><code>1 &lt;= nums[i] &lt;= 100</code></li>
</ul>

class Solution {
public:
    bool canPartition(vector<int>& nums) {
        int target = accumulate(nums.begin(), nums.end(), 0);

        if (target % 2) {
            return false;
        }

        vector<vector<char>> checkedSums(nums.size(), vector<char>(20000));

        return checkNums(checkedSums, nums, 0, target / 2);
    }

private:
    bool checkNums(vector<vector<char>>& checkedSums, vector<int>& nums, int from, int sum) {
        if (sum == 0) {
            return true;
        }

        if (sum < 0 || from == nums.size() || checkedSums[from][sum]) {
            return false;
        }

        checkedSums[from][sum] = 1;
        return checkNums(checkedSums, nums, from+1, sum) || checkNums(checkedSums, nums, from+1, sum-nums[from]);
    }
};
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