Left-hand string parsing

The left rotation operation of the string is to transfer several characters in front of the string to the end of the string, please define a function to complete the left rotation operation of the string

Input: abcdef 2
Output: cdefab

Input: abcdef 3
Output: defabc

Suppose that abcdef wants to rotate two left-handed to get cdefad.
Source: Jianzhi offer

The first method you can think of:

暴力求解法：每次左旋一个字符，左旋 k 次达到目标
或者优化一下
1、把 a b 拿出来
2、然后将剩余字符从字符串开头依次放置
3、把 a b 添加到字符串末尾

Although this method can be easily thought of, it is not the optimal solution

The optimization of the left-handed process is as follows:

1. Divide the target string (abcdef) into two parts according to the number of digits to be left-handed.

2. Reverse the first half and the second half respectively, and get the following results.

3. Reverse the entire string to get the character after the left-handed 2 digits. string

According to the above analysis steps, we first need to implement a function to reverse the string

Reverse string function:

void reverse(char* left, char* right) {
    
    
	assert(left && right);

	while (left < right) {
    
    
		char temp = *left;
		*left++ = *right;
		*right-- = temp;
	}
}

Then implement the left-handed string function:

void rotate_left(char* str, int k) {
    
    
	assert(str);
	int len = strlen(str);
	assert(k <= len);//k不能超过数组的长度
	//反转前半部分
	reverse(str, str + k - 1);
	//反转后半部分
	reverse(str + k, str + len - 1);
	//反转整体
	reverse(str, str + len - 1);
}