Leetcode question brushing: String 05 (Sword finger offer 58 - ii. left rotation string)

subject ： The finger of the sword Offer58-II. Left rotation string

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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".

Example 1：
Input : s = “abcdefg”, k = 2
Output : “cdefgab”

Example 2：
Input : s = “lrloseumgh”, k = 6
Output : “umghlrlose”

Limit ：
1 <= k < s.length <= 10000

As soon as this question is brought up , It takes brains ？

    public String reverseLeftWords1(String s, int n) {
    
        // Intercept the first left of the current string n position 
        String head = s.substring(0, n);
        return s.substring(n) + head;
    }

Let's look at the solution

Do it again according to the idea of problem solving .

   public String reverseLeftWords(String s, int n) {
    
        StringBuilder result = new StringBuilder(s);
        // Reverse the first half 
        reverseStr(result, 0, n);
        // Reverse the second half 
        reverseStr(result, n, s.length());
        // Reverse entire segment 
        reverseStr(result, 0, s.length());
        return String.valueOf(result);
    }
    /** *  Inverts the string in the specified interval  * * @param s * @param start * @param end * @return */
    public static StringBuilder reverseStr(StringBuilder s, int start, int end) {
    
        while (start < end) {
    
            char temp = s.charAt(start);
            s.setCharAt(start, s.charAt(end - 1));
            s.setCharAt(end-1, temp);
            start++;
            end--;
        }
        return s;
    }

There is one saying. , I can't think of doing this without looking at the solution .