# 88.merge-sorted-array

## Statement

• Difficulty: Easy
• Tag: `数组` `双指针` `排序`

``````输入：nums1 = [1,2,3,0,0,0], m = 3, nums2 = [2,5,6], n = 3

``````

``````输入：nums1 = [1], m = 1, nums2 = [], n = 0

``````

``````输入：nums1 = [0], m = 0, nums2 = [1], n = 1

``````

• `nums1.length == m + n`
• `nums2.length == n`
• `0 <= m, n <= 200`
• `1 <= m + n <= 200`
• `-109 <= nums1[i], nums2[j] <= 109`

• Difficulty: Easy
• Tag: `Array` `Two Pointers` `Sorting`

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`

Follow up: Can you come up with an algorithm that runs in `O(m + n)` time?

## Solution

``````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.
"""

i = n + m - 1
j = m - 1
k = n - 1
while i >= 0:
if j < 0:
nums1[i] = nums2[k]
k -= 1
elif k < 0:
nums1[i] = nums1[j]
j -= 1
else:
if nums1[j] >= nums2[k]:
nums1[i] = nums1[j]
j -= 1
else:
nums1[i] = nums2[k]
k -= 1
i -= 1
``````