**based on the XOR equations:**

Given:

a ^ a = 0

b ^ 0 = b

and XOR, order does not match

**Then:**

a ^ b ^ a = (a ^ a) ^ b = 0 ^ b = b, is b is the number. all other pairs XOR equals 0

```
public char findTheDifference(String s, String t) {
int num = 0;
for (char c : s.toCharArray()) {
num ^= (c - 'a');
}
for (char c : t.toCharArray()) {
num ^= (c - 'a');
}
return (char)('a' + num);
}
```