88. Merged Sorted Array.py

"""
88. Merge Sorted Array

You are given two integer arrays nums1 and nums2, sorted in non-decreasing order, and two integers m and n,
representing the number of elements in nums1 and nums2 respectively.
Merge nums1 and nums2 into a single array sorted in non-decreasing order.
The final sorted array should not be returned by the function, but instead be stored inside the array nums1. 
To accommodate this, nums1 has a length of m + n, where the first m elements denote the elements that should be merged,
and the last n elements are set to 0 and should be ignored. nums2 has a length of n.

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

Example 2:
Input: nums1 = [1], m = 1, nums2 = [], n = 0
Output: [1]
Explanation: The arrays we are merging are [1] and [].
The result of the merge is [1].

Example 3:
Input: nums1 = [0], m = 0, nums2 = [1], n = 1
Output: [1]
Explanation: 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.
 

Constraints:
nums1.length == m + n
nums2.length == n
0 <= m, n <= 200
1 <= m + n <= 200
-109 <= nums1[i], nums2[j] <= 109
"""

class Solution:
    def merge(self, nums1: List[int], m: int, nums2: List[int], n: int) -> None:
        # Initialize pointers for nums1 and nums2
        p1 = m - 1
        p2 = n - 1
        
        # Initialize pointer for the end of nums1
        p = m + n - 1
        
        # While there are elements in both arrays
        while p1 >= 0 and p2 >= 0:
            if nums1[p1] > nums2[p2]:
                # Move the larger element from nums1 to the end of nums1
                nums1[p] = nums1[p1]
                p1 -= 1
            else:
                # Move the larger element from nums2 to the end of nums1
                nums1[p] = nums2[p2]
                p2 -= 1
            # Move pointer for the end of nums1 to the left
            p -= 1
        
        # If there are remaining elements in nums2, copy them to nums1
        nums1[:p2 + 1] = nums2[:p2 + 1]