Description Link to heading

88.merge-sorted-array

Solution Link to heading

We use pointers, assign values of nums1 from end to front, so we use only $\Theta(1)$ extra space.

Code Link to heading 

#include <vector>
using std::vector;
class Solution {
    public:
    void merge(vector<int>& nums1, int m, vector<int>& nums2, int n) {
        int p1 = m - 1, p2 = n - 1;
        int idx = m + n - 1;
        for (int idx = m + n - 1; idx >= 0; idx--) {
            if (p1 < 0)
                nums1[idx] =  nums2[p2--];
            else if (p1 >= 0 && p2 >= 0) {
                if (nums1[p1] > nums2[p2])
                    nums1[idx] = nums1[p1--];
                else
                    nums1[idx] = nums2[p2--];
            }
        }
    }
};