Algorithm OJ questions (1)

1. Remove duplicates in a sorted array

Original link: https://leetcode.cn/problems/remove-duplicates-from-sorted-array/

 

 

 Idea: Using double pointer algorithm can make the time complexity reach O(1).

The specific process: (explained by drawing)

 

 Code:

int removeDuplicates(int* nums, int numsSize)
{
    if(numsSize==0)
        return 0;
	int i=0,j=1;
    int dst=0;
    while(j<numsSize)
    {
        if(nums[i]==nums[j])
        {
            ++j;
        }
        else
        {
            nums[dst]=nums[i];
            dst++;
            i=j;
            j++;
        }
    } 
    nums[dst]=nums[i];
    dst++;
    return dst;
}

2. Merge two sorted arrays

   Original title link: https://leetcode.cn/problems/merge-sorted-array/

 Idea: double pointer arithmetic

Implementation process:

Define two variables end1, end2, respectively point to the last element of the two arrays

Compare the size of num1[end1] and num2[end2], and move the larger value to array one in turn, from the back to the front

As shown below:

 Code:

void merge(int* nums1, int nums1Size, int m, int* nums2, int nums2Size, int n)
{
    int end1=m-1,end2=n-1;
    int end=m+n-1;
    while(end1>=0&&end2>=0)
    {
        if(nums1[end1]>nums2[end2])
        {
            nums1[end--]=nums1[end1--];
        }
        else
        {
            nums1[end--]=nums2[end2--];
        }
    }
    while(end2>=0)
    {
        nums1[end--]=nums2[end2--];
    }
}