Double pointer Foundation

One 、 Double pointer

Double pointers are mainly used to traverse arrays , Two pointers point to different elements , Work together , Generally speaking, they are all in the same array .

Two 、 classification

According to the different problems , The direction of movement of the pointer will also be different , It can be divided into two situations ：

• Traversal direction is the same and will not intersect
  This kind of situation is generally used to solve the problem of searching a certain interval of the array , Also known as the sliding window problem .
• The traversal direction is opposite and the array itself is orderly
  This situation is generally used for element search

Applications can be divided into ：

1. Two number sum problem
2. Merge two ordered arrays
3. Speed pointer problem
4. Sliding window problem

3、 ... and 、 A basic review of pointers

• const Heel int, Value cannot be changed , Pointer can be changed

const int * p2 = &x  

• const Followed by a pointer p3 front , Value can be changed , The pointer cannot be changed

int * const p3 = &x

• const Heel int And a pointer p4, Value can be changed , The pointer cannot be changed

const int  * const  p4 = &x 

• * Left Union , Therefore, it is a function whose return type is pointer

int * function(){
    }

• ( ) hold * Included , And function combination , Therefore, it is return ; Pointer of type function

int func2(int a,int b){
    }
int (*function)(int,int) = func2;