Question swiping Madness - leetcode's sword finger offer58 - ii Detailed explanation of left rotation string

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Introduction to this article ：LeetCode Sword finger offer58 - II. Left rotation string Detailed explanation ！

Get to know the author ： Aspire to be a great programmer , Xiaobai, who is currently a sophomore in College .

Inspirational terms ： The tediousness of programming , Let's study together and become interesting ！

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List of articles

subject

Method One （ Circulation ）

Their thinking

Method （ One ） — Code

Method Two （ Three step reverse order method ）

Problem solving Ideas

Method （ Two ) — Code  

Conclusion

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subject

        The left rotation operation of string is to transfer several characters in front of string to the end of string . Please define a function to implement the left rotation operation of string . such as , Input string "abcdefg" And number 2, This function will return the result of rotating two bits to the left "cdefgab".

link ：https://leetcode.cn/problems/zuo-xuan-zhuan-zi-fu-chuan-lcof    source ： Power button （LeetCode）

Example 1：

 Input : s = "abcdefg", k = 2
 Output : "cdefgab"

Example 2：

 Input : s = "lrloseumgh", k = 6
 Output : "umghlrlose"

Method One （ Circulation ）

Their thinking

For a string, it's just left rotation , It is certain that this string can be changed , So it's not a constant string , We use arrays to represent , Secondly, we can take out every character before the string every time , Then take each character of the original string forward , Finally, put the characters taken out at the end of the string , For a cycle , How many characters to rotate is how many times to cycle ！

Let's draw a picture to explain ：

The idea should be clear ！ Now let's implement the code ：

Method （ One ） — Code

#include<stdio.h>
#include<assert.h>
#include<string.h>
void left_revolve(char arr[], int k)// Implementation function 
{
	assert(arr);// Assert , Prevent null pointer 
	int len = strlen(arr);// Total string length 
	// When k>len Time is the problem of reincarnation 
	k %= len;
	int i = 0;
	for (i = 0; i < k; i++)
	{
		char tmp = arr[0];// Take out the first character to store 
		int j = 0;
		for (j = 0; j < len - 1; j++)
		{
			arr[j] = arr[j + 1];// Replace character forward 
		}
		arr[len - 1] = tmp;
	}
}
int main()
{
	char arr[] = { "abcdefg" };
	int k = 0;
	scanf("%d", &k);// How many characters to rotate 
	// Realize its function with function 
	left_revolve(arr, k);
	printf("%s\n", arr);// Print the results 
	return 0;
}

Let's look at the results ：

Method Two （ Three step reverse order method ）

Problem solving Ideas

One ： We can first divide the string into two parts ,1. Is the string to rotate   2. The rest of the string .

Two ： Then put them in reverse order .

3、 ... and ： Finally, reverse the whole order

Let's draw a picture , The result of the person who gets the map ：

Method （ Two ) — Code  

#include<stdio.h>
#include<assert.h>
#include<string.h>
void reverse(char* left, char* right)// Reverse string function , It's a pointer 
{
	assert(left && right);
	while (left < right)
	{
		char tmp = *left;// Back and forth 
		*left = *right;
		*right = tmp;
		left++;
		right--;
	}

}
void left_revolve(char arr[], int k)
{
	assert(arr);
	// Reverse string 
	int len = strlen(arr);
	k %= len;
	reverse(arr, arr + k - 1);// String to rotate left in reverse order 
	reverse(arr + k, arr + len - 1);// The remaining strings in reverse order 
	reverse(arr, arr + len - 1);// Reverse the entire string 
}
int main()
{
	char arr[] = { "abcdefg" };
	int k = 0;
	scanf("%d", &k);
	left_revolve(arr, k);
	printf("%s", arr);
	return 0;
}

Look at the results ：

Conclusion

Ok! At this point, the blog is finished , What's wrong or bad , Please help readers correct （ Just leave a comment below ）, Thank you all ！