<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 sum = 0;
        int n = nums.size();
        for (int i = 0; i < n; ++i) {
            sum += nums[i];
        }
        if (sum % 2 != 0)
            return false;

        int target = sum / 2;
        unordered_set<int> vs;
        vs.insert(0);
        bool res = false;
        for (int i = n - 1; i >= 0; --i) {
            unordered_set<int> vscopy = vs;
            for (auto itr = vscopy.begin(); itr != vscopy.end(); itr++) {
                vs.insert(*itr + nums[i]);
                if (vs.contains(target)) {
                    res = true;
                    break;
                }
            }
            if (res)
                return res;
        }
        return false;
    }
};
208266