MergeSortedArray.py

"""
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.

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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


Follow up: Can you come up with an algorithm that runs in O(m + n) time?
"""
from typing import List


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.
        """
        # Initialize two pointers, one for nums1 and one for nums2 from the end
        p1, p2 = m - 1, n - 1

        # Initialize a pointer for the end of nums1
        p = m + n - 1

        # Start from the end of both arrays and merge in non-decreasing order
        while p1 >= 0 and p2 >= 0:
            if nums1[p1] > nums2[p2]:
                nums1[p] = nums1[p1]
                p1 -= 1
            else:
                nums1[p] = nums2[p2]
                p2 -= 1
            p -= 1
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            # print(nums1)
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        # If there are remaining elements in nums2, copy them to nums1
        while p2 >= 0:
            nums1[p] = nums2[p2]
            p2 -= 1
            p -= 1


# Define a function to test the merge method
def test_merge():
    # Test case 1
    nums1 = [1, 2, 3, 0, 0, 0]
    m = 3
    nums2 = [2, 5, 6]
    n = 3
    print(f"nums1: {nums1}")
    print(f"nums2: {nums2}")
    print(f"m: {m}")
    print(f"n: {n}")
    solution = Solution()
    solution.merge(nums1, m, nums2, n)
    print(nums1)  # Expected output: [1, 2, 2, 3, 5, 6]

    # Test case 2
    nums1 = [1]
    m = 1
    nums2 = []
    n = 0
    print(f"nums1: {nums1}")
    print(f"nums2: {nums2}")
    print(f"m: {m}")
    print(f"n: {n}")
    solution = Solution()
    solution.merge(nums1, m, nums2, n)
    print(nums1)  # Expected output: [1]

    # Test case 3
    nums1 = [0]
    m = 0
    nums2 = [1]
    n = 1
    print(f"nums1: {nums1}")
    print(f"nums2: {nums2}")
    print(f"m: {m}")
    print(f"n: {n}")
    solution = Solution()
    solution.merge(nums1, m, nums2, n)
    print(nums1)  # Expected output: [1]

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    # Test case 4
    nums1 = [1, 2, 3, 0, 0, 0, 4]
    m = 3
    nums2 = [2, 5, 6]
    n = 3
    print(f"nums1: {nums1}")
    print(f"nums2: {nums2}")
    print(f"m: {m}")
    print(f"n: {n}")
    solution = Solution()
    solution.merge(nums1, m, nums2, n)
    print(nums1)  # Expected output: [1, 2, 2, 3, 5, 6]

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if __name__ == "__main__":
    test_merge()