[Array]Merge Sorted Array

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 nums1 and nums2 are m and n respectively.

方法1： 开辟新数组进行归并操作。额外的存储空间为O(m+n)；

class Solution {
public:
    void merge(vector<int>& nums1, int m, vector<int>& nums2, int n) {
        vector<int> res ;
        int i=0,j=0;
        while(i<m&&j<n){
            if(nums1[i]<nums2[j]){
                res.push_back(nums1[i]);
                i++;
            }
            else{
                res.push_back(nums2[j]);
                j++;
            }
        }
        while(i<m){
            res.push_back(nums1[i]);
            i++;
        }
        while(j<n){
            res.push_back(nums2[j]);
            j++;
        }
        nums1=res;
    }
};

方法2： 因为nums1数组有足够的空间，所以利用这点从尾部开始从大到小进行排序。额外的存储空间为O(1)。

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