<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 = accumulate(nums.begin(), nums.end(), 0);
        if (sum % 2) {
            return false;
        }
        unordered_set<int> reachable;
        reachable.insert(0);
        for (int i = 0; i < nums.size(); i++) {
            unordered_set<int> temp;
            for (int num : reachable) {
                if (num+nums[i] == sum/2) {
                    return true;
                }
                temp.insert(num+nums[i]);
            }
            reachable.merge(temp);
        }
        return false;

        /*
        vector<vector<bool>> canReach(nums.size()+1, vector<bool>(sum/2+1));
        canReach[0][0] = true;
        for (int i = 1; i <= nums.size(); i++) {
            for (int j = 0; j <= sum/2; j++) {
                canReach[i][j] = canReach[i-1][j];
                if (j-nums[i-1] >= 0) {
                    canReach[i][j] = canReach[i][j] || canReach[i-1][j-nums[i-1]];
                }
            }
        }
        return canReach[nums.size()][sum/2];
        */
    }
};
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