<p>Given an unsorted integer array <code>nums</code>. Return the <em>smallest positive integer</em> that is <em>not present</em> in <code>nums</code>.</p>

<p>You must implement an algorithm that runs in <code>O(n)</code> time and uses <code>O(1)</code> auxiliary space.</p>

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

<pre>
<strong>Input:</strong> nums = [1,2,0]
<strong>Output:</strong> 3
<strong>Explanation:</strong> The numbers in the range [1,2] are all in the array.
</pre>

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

<pre>
<strong>Input:</strong> nums = [3,4,-1,1]
<strong>Output:</strong> 2
<strong>Explanation:</strong> 1 is in the array but 2 is missing.
</pre>

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

<pre>
<strong>Input:</strong> nums = [7,8,9,11,12]
<strong>Output:</strong> 1
<strong>Explanation:</strong> The smallest positive integer 1 is missing.
</pre>

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

<ul>
	<li><code>1 &lt;= nums.length &lt;= 10<sup>5</sup></code></li>
	<li><code>-2<sup>31</sup> &lt;= nums[i] &lt;= 2<sup>31</sup> - 1</code></li>
</ul>

class SPV {
private:
    vector<int> mVec;
    void removeNegatives() {
        vector<int> positiveVec{};
        for (auto& v : mVec) {
            if (v>0) {
                positiveVec.push_back(v);
            }
        }
        mVec = positiveVec;
    }
    void sortVec() {
        sort(mVec.begin(), mVec.end());
    }
public:
    SPV(vector<int> nums) : mVec(nums) {
        removeNegatives();
        sortVec();
    } 
    int firstMissingPositive() {
        int i=0;
        if (mVec[0] != 1) {
            return 1;
        }
        while (i+1<mVec.size() && (mVec[i+1]-mVec[i] == 1 || mVec[i+1]==mVec[i])) {
            ++i;
        }
        return mVec[i]+1;
    }
};

class Solution {
public:
    int firstMissingPositive(vector<int>& nums) {
        SPV spv = SPV{nums};
        return spv.firstMissingPositive();
    }
};
57200