# Merge Sorted Array

Given two sorted integer arrays *nums1 \_and \_nums2*, merge \_nums2 \_into \_nums1 \_as one sorted array.

**Note:**

* The number of elements initialized in \_nums1 \_and \_nums2 \_are \_m \_and \_n \_respectively.
* You may assume that *nums1 \_has enough space (size that is greater or equal to \_m* + *n* ) to hold additional elements from

  *nums2*.

**Example:**

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

Output: [1,2,2,3,5,6]
```

从后往前做，不用开辟新空间

```python
    def merge(self, nums1, m, nums2, n):
        """
        :type nums1: List[int]
        :type m: int
        :type nums2: List[int]
        :type n: int
        :rtype: void Do not return anything, modify nums1 in-place instead.
        """
        idx = m + n - 1
        m -= 1
        n -= 1
        while m >= 0 and n >= 0:
            if nums1[m] > nums2[n]:
                nums1[idx] = nums1[m]
                m -= 1
            else:
                nums1[idx] = nums2[n]
                n -= 1
            idx -= 1

        if m < 0:
            nums1[:n + 1] = nums2[:n + 1]

        return
```
