[C language] string reverse order implementation (recursion and iteration)

One 、 Thought analysis

1. Analysis of iteration method

2. Thinking analysis of recursive method （ Under very, very limited parameters ）

3. Analysis of optimized recursive method （ Sufficient parameters ）

Two 、 Code demonstration

// Reverse string order 
#include <stdio.h>
#include <string.h>
// Method ① Circulation 
void reverse1(char* arr,int sz)
{
    
	int left = 0, right = sz - 2;
	char t;
	while (left <= right)
	{
    
		t = arr[left];
		arr[left] = arr[right];
		arr[right] = t;
		left++;
		right--;
	}
}
// Method ② recursive （ With very few parameters , Allow library functions strlen）
void reverse2(char* str)
{
    
	char tmp = *str;
	int len = strlen(str);
	*str = *(str + len - 1);
	*(str + len - 1) = '\0';
	if (strlen(str + 1) >= 2)
		reverse2(str + 1);
	*(str + len - 1) = tmp;
}
// Method ③ Recursive method （ Sufficient parameters ）
void reverse3(char* arr, int left,int right)
{
    
	char tmp = arr[left];
	arr[left] = arr[right];
	arr[right] = tmp;// There is no need to zero the string 
	if(left<right)
		reverse3(arr, left + 1, right - 1);
}
int main()
{
    
	char arr1[] = "abcdef";
    char arr2[] = "abcdef";
    char arr3[] = "abcdef";
	int sz1 = sizeof(arr1) / sizeof(arr1[0]);
    int sz2 = sizeof(arr2) / sizeof(arr2[0]);
	int sz3 = sizeof(arr3) / sizeof(arr3[0]);
    reverse1(arr1, sz1);
	reverse2(arr2);
	reverse3(arr3, 0, sz3 - 2);
	printf("%s\n", arr1);
    printf("%s\n", arr2);
    printf("%s\n", arr3);
	return 0;
}