## Question

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`

## Algorithm

- Read question carefully to understand what's the requirements;
- Handle edge case; (thanks to the examples)
- Start from the end then you can do the comparison and set in one pass, because the last n digits of nums1 has been pre occupied for you to set new values

## Code

class Solution { public void merge(int[] nums1, int m, int[] nums2, int n) { if (n == 0) return; if (m == 0) { for (int i = 0; i < m + n; i++) { nums1[i] = nums2[i]; } return; } int i = m - 1, j = n - 1; while (i >= 0 && j >= 0) { if (nums2[j] > nums1[i]) { nums1[i + j + 1] = nums2[j--]; } else { nums1[i + j + 1] = nums1[i--]; } } while (j >= 0) { nums1[j] = nums2[j--]; } } }