Leetcode- find a difference - simple

title ：389 Make a difference - Simple

subject

Given two strings s and t, They contain only lowercase letters .

character string *t* By string *s* Random rearrangement , Then add a letter at random .

Please find out in t The letters added in .

Example 1

 Input ：s = "abcd", t = "abcde"
 Output ："e"
 explain ：'e'  It's the letter that was added .

Example 2

 Input ：s = "", t = "y"
 Output ："y"

Example 3

 Input ：s = "a", t = "aa"
 Output ："a"

Example 4

 Input ：s = "ae", t = "aea"
 Output ："a"

Tips

• 0 <= s.length <= 1000
• t.length == s.length + 1
• s and t Contains only lowercase letters

Code Java

//  Passed   But it's slow  14ms
public char findTheDifference(String s, String t) {
    
    if (s.length() == 0)
        return t.charAt(0);
    // 1  take s Elements in map to map in ,key Is element value ,value Yes, there are 
    // 2  take t Mapping to map in ,
    // 3  If it does not exist   Return this element directly ,  If there is, then value-1,  When it comes to 0 when , It means that there is no , Return this element 
    HashMap map = new HashMap();
    for (int i = 0; i < s.length(); i++) {
    
        Object get = map.get(s.charAt(i));
        if (get != null) {
    
            int count = (int) get + 1;
            map.put(s.charAt(i), count);
        } else {
    
            map.put(s.charAt(i), 1);
        }
    }
    for (int i = 0; i < t.length(); i++) {
    
        Object o = map.get(t.charAt(i));
        if (o == null)
            return t.charAt(i);
        else {
    
            int count = (int) o - 1;
            if (count < 0)
                return t.charAt(i);
            map.put(t.charAt(i), count);
        }
    }
    return 'F';
}
//  Relatively fast  3ms
public char findTheDifference1(String s, String t) {
    
    char[] chars = s.toCharArray();
    char[] chart = t.toCharArray();
    Arrays.sort(chars);
    Arrays.sort(chart);
    for (int i = 0; i < s.length(); i++) {
    
        if (chars[i] != chart[i])
            return chart[i];
    }
    return chart[s.length()];
}

//  Exclusive or two sets of data  2ms
public char findTheDifference2(String s, String t) {
    
    int sum = 0;
    for (int i = 0; i < s.length(); i++) {
    
        sum ^= s.charAt(i);
        sum ^= t.charAt(i);
    }
    sum ^= t.charAt(s.length());
    return (char) sum;
}