Merge Sorted Array

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

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.

Discussion

闭着眼睛也要写出来。看后面的follow up

Solution

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

Follow up

What if size of A >>>> size of B? We can use binary search to insert the smaller array.
而且在插入的时候返回插入的位置，这样下一个就不从全局搜索了。
It only cost O(mlogn) comparisons instead of O(n+m), much better.

What if B is in descending order? j从0开始就行了啊！