<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> merge(vector<int>& arr1, vector<int>& arr2){
    int n1=arr1.size();
    int n2=arr2.size();
    vector<int> arr(n1+n2);

    int i=0,j=0,k=0;
    while(i<n1 && j<n2){
        if(arr1[i]<=arr2[j]){
            arr[k]= arr1[i];
            i++;k++;
        }
        else{
            arr[k]=arr2[j];
            j++;k++;
        }
    }
    while(i<n1){
            arr[k]= arr1[i];
            i++;k++;
    }
    while(j<n2){
            arr[k]= arr2[j];
            j++;k++;
    }
    return arr;
}
vector<int> mergesort(vector<int>&arr, int start, int end){
    // cout<< start <<" "<<end<< " "; 
    if(start>=end) return {arr[start]};
    vector<int> arr1= mergesort(arr, start, (start+end)/2);
    vector<int> arr2= mergesort(arr, (start+end)/2 +1, end);
    vector<int> mergedArray = merge(arr1, arr2);
    return mergedArray;
}
    vector<int> sortArray(vector<int>& nums) {
        int n=nums.size();
        return mergesort(nums,0,n-1);
    }
};
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