Array - 88. Merge Sorted Array

88. 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:

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

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

思路：

主要体现一个倒着复制的思想，在c语言自带排序源码包里就有不少倒着复制的思想。
两个数组有序，合并完有序，只要从最后一位开始往前复制就可以保证O(m +n) 的时间复杂度完成。
就是每次取两个数组的最大值往后放就行。

代码：

java：

class Solution {

    public void merge(int[] nums1, int m, int[] nums2, int n) {
        int i = m - 1, j = n -1, k = m + n - 1;
        while (i >= 0 && j >= 0) 
            nums1[k--] = nums1[i] >= nums2[j] ? nums1[i--] : nums2[j--];
        
        while (j >= 0)
            nums1[k--] = nums2[j--];
    }
}

golang:

func merge(nums1 []int, m int, nums2 []int, n int)  {
    k := n + m - 1
    i := m - 1
    j := n - 1
    for i >= 0 && j >= 0 {
        if nums1[i] < nums2[j] {
            nums1[k] = nums2[j]
            j--
        } else {
            nums1[k] = nums1[i]
            i--
        }
        k--
    }
    
    for j >= 0 {
        nums1[k] = nums2[j]
        k--
        j--
    }
}