<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:
void merge(vector<int>& arr, int s, int e) {

    int mid = s+(e-s)/2;

    int len1 = mid - s + 1;
    int len2 = e - mid;

    int *first = new int[len1];
    int *second = new int[len2];

    int mainArrayIndex = s;
    for(int i=0; i<len1; i++) {
        first[i] = arr[mainArrayIndex++];
    }

    mainArrayIndex = mid+1;
    for(int i=0; i<len2; i++) {
        second[i] = arr[mainArrayIndex++];
    }
   
    int index1 = 0;
    int index2 = 0;
    mainArrayIndex = s;

    while(index1 < len1 && index2 < len2) {
        if(first[index1] < second[index2]) {
            arr[mainArrayIndex++] = first[index1++];
        }
        else{
            arr[mainArrayIndex++] = second[index2++];
        }
    }   

    while(index1 < len1) {
        arr[mainArrayIndex++] = first[index1++];
    }

    while(index2 < len2 ) {
        arr[mainArrayIndex++] = second[index2++];
    }

    delete []first;
    delete []second;

}

void mergeSort(vector<int>& arr, int s, int e) {

    if(s >= e) {
        return;
    }
    
    int mid = s+(e-s)/2;

    mergeSort(arr, s, mid);
   
    mergeSort(arr, mid+1, e);

    merge(arr, s, e);

}

    vector<int> sortArray(vector<int>& arr) {
        
        int n=arr.size();
        mergeSort(arr,0,n-1);
        return arr;
    }
};
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