题目

解题代码

class Solution {
    public boolean buddyStrings(String s, String goal) {
        if(s.length() != goal.length() ) return false;
        Set<Character> set = new HashSet<>();
        for(int i = 0; i < s.length(); i++ ) {
            set.add(s.charAt(i) );
        }
        //1 <= s.length, goal.length <= 2 * 104
        if(s.equals(goal) && s.length() != set.size() ) return true;
        int time = 0,first = 0, seconds = 0;
        for(int i = 0; i < s.length(); i++ ) {
            if(s.charAt(i) != goal.charAt(i)) {
                if(time == 2) return false; //出现三次以上不同字符，返回false
                if(time == 1) seconds = i; //第二次出现，记录位置
                if(time == 0) first = i; //第一次不一样
                time ++ ;
            }
        }
        if(time == 0) return false;
        if(s.charAt(first) == goal.charAt(seconds)  && s.charAt(seconds) == goal.charAt(first) ) return true;
        return false;
    }
}