<p>Given an array of integers <code>nums</code>, sort the array in ascending order and return it.</p>

<p>You must solve the problem <strong>without using any built-in</strong> functions in <code>O(nlog(n))</code> time complexity and with the smallest space complexity possible.</p>

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

<pre>
<strong>Input:</strong> nums = [5,2,3,1]
<strong>Output:</strong> [1,2,3,5]
<strong>Explanation:</strong> After sorting the array, the positions of some numbers are not changed (for example, 2 and 3), while the positions of other numbers are changed (for example, 1 and 5).
</pre>

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

<pre>
<strong>Input:</strong> nums = [5,1,1,2,0,0]
<strong>Output:</strong> [0,0,1,1,2,5]
<strong>Explanation:</strong> Note that the values of nums are not necessairly unique.
</pre>

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

<ul>
	<li><code>1 &lt;= nums.length &lt;= 5 * 10<sup>4</sup></code></li>
	<li><code>-5 * 10<sup>4</sup> &lt;= nums[i] &lt;= 5 * 10<sup>4</sup></code></li>
</ul>

class Solution {
public:
    vector<int> sortArray(vector<int>& nums) {
        mergeSort(nums, 0, nums.size() - 1);
        return nums;
    }
    void merge(vector<int>& arr, int left, int mid, int right){
        int subarr1 = mid - left + 1;
        int subarr2 = right - mid;
        vector<int>* leftarr = new vector<int>(subarr1);
        vector<int>* rightarr = new vector<int>(subarr2);

        for(int i = 0; i < subarr1; i++ ){
            (*leftarr)[i] = arr[left + i];
        }
        for (int j = 0; j < subarr2; j++){
            (*rightarr)[j] = arr[mid + 1 + j];
        }
        int index_of_subarr1 = 0, index_of_subarr2 = 0;
        int index_of_merged_arr = left;

        while (index_of_subarr1 < subarr1 && index_of_subarr2 < subarr2){
            if ((*leftarr)[index_of_subarr1] <= (*rightarr)[index_of_subarr2]){
                arr[index_of_merged_arr] = (*leftarr)[index_of_subarr1];
                index_of_subarr1++;
            }
            else{
                arr[index_of_merged_arr] = (*rightarr)[index_of_subarr2];
                index_of_subarr2++;
            }
            index_of_merged_arr++;
        }

        //if anything is left
        while(index_of_subarr1 < subarr1){
            arr[index_of_merged_arr] = (*leftarr)[index_of_subarr1];
            index_of_merged_arr++;
            index_of_subarr1++;
        }

        while(index_of_subarr2 < subarr2){
            arr[index_of_merged_arr] = (*rightarr)[index_of_subarr2];
            index_of_merged_arr++;
            index_of_subarr2++;
        }

        delete leftarr;
        delete rightarr;
    }

    void mergeSort(vector<int>& arr, int begin, int end){
        if (begin >= end){
            return;
        }
        int mid = begin + (end - begin) / 2;
        mergeSort(arr, begin, mid);
        mergeSort(arr, mid + 1, end);
        merge(arr, begin, mid, end);
    }
};
268501