88. Merge Sorted Array

题目

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 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]

Constraints:

• -10^9 <= nums1[i], nums2[i] <= 10^9
• nums1.length == m + n
• nums2.length == n

题目大意

合并两个已经有序的数组，结果放在第一个数组中，第一个数组假设空间足够大。要求算法时间复杂度足够低。

解题思路

为了不大量移动元素，就要从2个数组长度之和的最后一个位置开始，依次选取两个数组中大的数，从第一个数组的尾巴开始往头放，只要循环一次以后，就生成了合并以后的数组了。

代码

package leetcode

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