<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 {
unordered_map<int, unordered_set<int>> dp;

    int sumArr(vector<int>& nums) {
        int s = 0;
        for (int n : nums) s += n;
        return s;
    }

    bool seenBefore(int index, int target) {
        return dp.find(index) != dp.end() &&
            dp[index].find(target) != dp[index].end();
    }

    bool canGetTarget(vector<int>& nums, int index, int target) {
        if (target < 0) return false;
        if (seenBefore(index, target)) return false; 
        if (index == nums.size()) return target == 0;
        if (
            canGetTarget(nums, index+1, target-nums[index]) ||
            canGetTarget(nums, index+1, target)
        ) {
            return true;
        }
        dp[index].insert(target);
        return false;
    }

public:
    bool canPartition(vector<int>& nums) {
        int arrSum = sumArr(nums);
        if (arrSum & 1) return false;
        int target = arrSum / 2; 
        return canGetTarget(nums, 0, target);
    }
};
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