344. Reverse string

Title Description ： Write a function , Its function is to invert the input string . Input string as character array char[] Given in the form of .

Limit ： Do not allocate extra space to another array , You have to modify the input array in place 、 Use O(1) To solve this problem .

Ideas ： Double pointer , Point to the head and tail at the same time , Exchange two positions , And then shrink to the middle at the same time .

The method of exchanging two numbers

Method 1: Use temporary variables

C++
// Suppose the scenario is that calling this function can exchange the values of two numbers , So input parameter pointer and pass array are ok 
// But you can't pass values , Such as void swap(int x,int y)
void swap(int *x,int *y)
{
    
    int temp = *x;
    *x = *y;
    *y = temp;
}

For clarity , The following are all ways of using value passing .
Method 2： XOR operation using bit operation , Languages that support bit operations , This method is the most efficient .
principle ：a^ b ^ b=a

a = a ^ b;
b = a ^ b;
a = a ^ b;

Method 3： Using logical operations

a=a+b;
b=a-b
a=a-b;