프로그래머스 - 인덱스 바꾸기 (JAVA)

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class Solution {
    public String solution(String my_string, int num1, int num2) {
        
        StringBuilder sb = new StringBuilder(my_string);
        
        char first = my_string.charAt(num1);
        char second = my_string.charAt(num2);
        
        sb.setCharAt(num1, second);
        sb.setCharAt(num2, first);

        return sb.toString();
    }
}