Merge Sorted Array 解答

Question

Given two sorted integer arrays nums1 and nums2, merge nums2 into nums1 as one sorted array.

Note:
You may assume that nums1 has enough space (size that is greater or equal to m + n) to hold additional elements from nums2. The number of elements initialized in nums1and nums2 are m and n respectively.

Solution 1 Naive Way

Time complexity O(n), space cost O(n)

public class Solution {
    public void merge(int[] nums1, int m, int[] nums2, int n) {
        int[] originNums1 = Arrays.copyOf(nums1, m);
        int pointer1 = 0, pointer2 = 0, i = 0;
        while (pointer1 < m && pointer2 < n) {
            if (originNums1[pointer1] <= nums2[pointer2]) {
                nums1[i] = originNums1[pointer1];
                pointer1++;
            } else {
                nums1[i] = nums2[pointer2];
                pointer2++;
            }
            i++;
        }
        while (pointer1 < m) {
            nums1[i] = originNums1[pointer1];
            pointer1++;
            i++;
        }
        while (pointer2 < n) {
            nums1[i] = nums2[pointer2];
            pointer2++;
            i++;
        }
    }
}

Solution 2

The key to solve this problem is moving element of A and B backwards. If B has some elements left after A is done, also need to handle that case.

Time complexity O(n), space cost O(1)

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