【C】 Reverse string (two recursive ideas)

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Preface

Very simple reverse string implementation , Record a recursive idea that is not easy to think of ！

Fulfill the requirements ：

Invert the characters in the parameter string , Not in reverse order .

such as :

char arr[ ] = “abcdef”;

In reverse order, the contents of the array become ：fedcba

Ideas 1：

Grasp the core idea of recursion and make the event small , To reverse the entire string , You can first exchange the first and last characters in the string , Then reverse the middle string ;

And the middle string can be recursive again with the above idea , Until there is no string in the middle of the first and last characters ;

If you want to recurse the middle content as a string , You need to put one behind it \0, And because you want to put this \0, The first character cannot be placed at the end of the string to complete the exchange , At this point, you can store this character with an intermediate variable , Wait until the middle string recursion completes the reverse order , Then put the stored first character in the position of the last character .

#include<stdio.h>
#include<assert.h>
#include<string.h>
void reverse(char* str)
{
    
	assert(str);
	char tmp = *str;
	int len = strlen(str);
	*str = *(str + len - 1);

	*(str+len - 1) = '\0';

	if (my_strlen(str + 1) >= 2)
	{
    
		reverse(str + 1);
	}
	*(str + len - 1) = tmp;
}

int main()
{
    
	char arr[] = "abcdefg";
	reverse(arr);
	printf("%s\n", arr);

	return 0;
}

Ideas 2：

Implement a recursive function to exchange strings two by two .

#include<stdio.h>
#include<assert.h>
#include<string.h>
void reverse(char arr[], int left, int right)
{
    
	assert(arr);
	if (left < right)
	{
     
		char tmp = arr[left];
		arr[left] = arr[right];
		arr[right] = tmp;
		reverse(arr, left + 1, right - 1);
	}
}

int main()
{
    
	char arr[] = "abcdefg";
	int left = 0;
	int right = strlen(arr)-1;
	reverse(arr, left, right);

	printf("%s\n", arr);

	return 0;
}

Conclusion

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