description

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?

submission

impl Solution {
    // we merge them by pop elements from the second array, and fill the first
    // array backward. 
    pub fn merge(nums1: &mut Vec<i32>, mut m: i32, nums2: &mut Vec<i32>, n: i32) {
        // index - 1
        m -= 1;
        let mut idx = (m + n) as usize;
        while let Some(num) = nums2.pop() {
            // search the correct index to fill the poped element
            while m >= 0 && nums1[m as usize] > num {
                nums1[idx] = nums1[m as usize];
                m -= 1;
                idx -= 1;
            }
            // fill the poped element
            nums1[idx] = num;
            idx -= 1;
        }
    }
}