<p>You are given two integer arrays <code>nums1</code> and <code>nums2</code>, sorted in <strong>non-decreasing order</strong>, and two integers <code>m</code> and <code>n</code>, representing the number of elements in <code>nums1</code> and <code>nums2</code> respectively.</p>

<p><strong>Merge</strong> <code>nums1</code> and <code>nums2</code> into a single array sorted in <strong>non-decreasing order</strong>.</p>

<p>The final sorted array should not be returned by the function, but instead be <em>stored inside the array </em><code>nums1</code>. To accommodate this, <code>nums1</code> has a length of <code>m + n</code>, where the first <code>m</code> elements denote the elements that should be merged, and the last <code>n</code> elements are set to <code>0</code> and should be ignored. <code>nums2</code> has a length of <code>n</code>.</p>

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

<pre>
<strong>Input:</strong> nums1 = [1,2,3,0,0,0], m = 3, nums2 = [2,5,6], n = 3
<strong>Output:</strong> [1,2,2,3,5,6]
<strong>Explanation:</strong> The arrays we are merging are [1,2,3] and [2,5,6].
The result of the merge is [<u>1</u>,<u>2</u>,2,<u>3</u>,5,6] with the underlined elements coming from nums1.
</pre>

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

<pre>
<strong>Input:</strong> nums1 = [1], m = 1, nums2 = [], n = 0
<strong>Output:</strong> [1]
<strong>Explanation:</strong> The arrays we are merging are [1] and [].
The result of the merge is [1].
</pre>

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

<pre>
<strong>Input:</strong> nums1 = [0], m = 0, nums2 = [1], n = 1
<strong>Output:</strong> [1]
<strong>Explanation:</strong> The arrays we are merging are [] and [1].
The result of the merge is [1].
Note that because m = 0, there are no elements in nums1. The 0 is only there to ensure the merge result can fit in nums1.
</pre>

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

<ul>
	<li><code>nums1.length == m + n</code></li>
	<li><code>nums2.length == n</code></li>
	<li><code>0 &lt;= m, n &lt;= 200</code></li>
	<li><code>1 &lt;= m + n &lt;= 200</code></li>
	<li><code>-10<sup>9</sup> &lt;= nums1[i], nums2[j] &lt;= 10<sup>9</sup></code></li>
</ul>

<p>&nbsp;</p>
<p><strong>Follow up: </strong>Can you come up with an algorithm that runs in <code>O(m + n)</code> time?</p>

class Solution:
    def merge(self, nums1: List[int], m: int, nums2: List[int], n: int) -> None:
        """
        Do not return anything, modify nums1 in-place instead.
        """

        # working backwards

        p1 = m - 1
        p2 = n - 1

        i = len(nums1) - 1

        if m == 0:
            for j in range(len(nums2)):
                nums1[j] = nums2[j]
        else:
            while i >= 0:
                if p2 < 0:
                    break
                elif p1 < 0:
                    nums1[i] = nums2[p2]
                    i -= 1
                    p2 -= 1
                elif nums1[p1] < nums2[p2]:
                    nums1[i] = nums2[p2]
                    i -= 1
                    p2 -= 1
                else:
                    nums1[i] = nums1[p1]
                    i -= 1
                    p1 -= 1
        


        
16200