[Leetcode] Merge Sorted Array

Problem

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.

Analysis

• 题目是把两个sorted的数组合并成一个，这里假设数组1足够大，所以直接合并到数组1
• 记录当前要写入的index，初始值为 m+n-1
• 对两个数组从后往前扫描
• 谁比较大，谁就先写入
• 同时update index
• Time: O(m+n)
• Space: O(1)

Code

	public class Solution {
	public void merge(int[] nums1, int m, int[] nums2, int n) {
	int idx = m+n-1;
	int i = m-1;
	int j = n-1;
	//fill in reverse order
	//larger one first
	while(i>=0 && j>=0){
	if(nums1[i]<nums2[j]){
	nums1[idx--] = nums2[j--];
	}else{
	nums1[idx--] = nums1[i--];
	}
	}
	//fill the rest of nums2
	while(j>=0){
	nums1[idx--] = nums2[j--];
	}
	}
	}

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Reference
[1] https://leetcode.com/problems/merge-sorted-array/