Merge Sorted Array
The key idea
Merge from the back. The last
n slots of nums1 are empty padding, so write the largest remaining element into the end first. Walking three pointers from the right (i over nums1, j over nums2, k at the write position) lets you fill in place with O(1) extra space, because the write position k is always at or to the right of the read pointer i — you never overwrite a value you still need.Problem
You are given two integer arrays nums1 and nums2, both 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.
Constraints
nums1.length == m + nnums2.length == n0 <= m, n <= 2001 <= m + n <= 200-10^9 <= nums1[i], nums2[j] <= 10^9
Examples
Input: nums1 = [1,2,3,0,0,0], m = 3, nums2 = [2,5,6], n = 3
Output: [1,2,2,3,5,6]
Input: nums1 = [1], m = 1, nums2 = [], n = 0
Output: [1]
Input: nums1 = [0], m = 0, nums2 = [1], n = 1
Output: [1]
Complexity
Time: O(m + n) Space: O(1)
See the full solution
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