Question making note 3 (two point search)

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subject

subject

One 、 In order to find

class Solution {
    
public:
    int search(vector<int>& nums, int target) {
    
        int n = nums.size();
        int a = -1;
        for(int i=0;i<n;i++)
        {
    
            if (nums[i] == target)
            {
    
               
                a = i;
            }
        }
        return a;
    }
};

Two 、 Two points search

1. Code

class Solution {
    
public:
    int search(vector<int>& nums, int target) {
    
        int min = 0;
        int max = nums.size() - 1;
        int mid = 0;
        while (min <= max)
        {
    
            mid = min + (max - min) / 2;
            if (nums[mid] > target)
            {
    
                max = mid - 1;

            }
            else if (nums[mid] < target)
            {
    
                min = mid + 1;

            }
            else if (nums[mid] == target)
            {
    

                return mid;
            }
        }
        return -1;
    }
};

2. Array subscript out of bounds and memory overflow

1） In the above topic , use max+min Risk of memory overflow , When two int Type variable addition , The result may be greater than int The maximum range that type can represent .
2） The subscript of the array is out of bounds , Because the memory that does not belong to the array is accessed , For example, an array with three elements is applied a[3], If you visit a[3] It will cause the subscript to cross the boundary , because a[3] Does not belong to this array .