389. Find the Difference (Easy)

https://leetcode.com/problems/find-the-difference/

Given two strings s and t which consist of only lowercase letters.

String t is generated by random shuffling string s and then add one more letter at a random position.

Find the letter that was added in t.

Example:

Input:
s = "abcd"
t = "abcde"

Output:
e

Explanation:
'e' is the letter that was added.

Solutions

class Solution {

    public char findTheDifference(String s, String t) {

        Map<Character, Integer> occurrence = new HashMap<>();

        for (int i = 0; i < s.length(); i++) {
            Character c = s.charAt(i);
            if (!occurrence.containsKey(c)) {
                occurrence.put(c, 0);
            }

            occurrence.put(c, occurrence.get(c) + 1);
        }

        for (int i = 0; i < t.length(); i++) {
            Character c = t.charAt(i);
            if (!occurrence.containsKey(c) || occurrence.get(c) == 0) {
                return c;
            }

            occurrence.put(c, occurrence.get(c) - 1);
        }

        return 'a';
    }
}

Incorrect Solutions

References