class Solution {

public char findTheDifference(String s, String t) {

// approach 1 : hashmap :- make a hashmap and store characters of s string and check in t string which is not in hashmap so that character is added

HashMap<Character,Integer> map = new HashMap<>();

for(int i=0;i<s.length();i++){

char ch = s.charAt(i);

if(map.containsKey(ch)){

map.put(ch,map.get(ch)+1);

}else{

map.put(ch,1);

}

}

for(int i=0;i<t.length();i++){

char ch = t.charAt(i);

if(map.containsKey(ch)){

// Subtract the value from the existing value

int newValue = map.get(ch) - 1;

// Update the HashMap with the new value

map.put(ch , newValue);

if(map.get(ch)<0){

return ch;

}

}else{

return ch;

}

}

return 0;

// approach 2 : take the sum of all characters in ascii value s and t separately and than subtract t - s and return that result after converting in char

int sum_s = 0;

for(int i=0;i<s.length();i++){

char c = s.charAt(i);

int asciiValue = (int) c;

sum_s += asciiValue;

}

int sum_t = 0;

for(int i=0;i<t.length();i++){

char c = t.charAt(i);

int asciiValue = (int) c;

sum_t += asciiValue;

}

int difference = sum_t - sum_s;

char ch = (char) difference;

return ch;

// approach 3 : using xor :-

int xor = 0;

for(int i=0;i<s.length();i++){

char ch = s.charAt(i);

xor ^= ch;

}

for(int i=0;i<t.length();i++){

char ch = t.charAt(i);

xor ^= ch;

}

return (char) xor;

}

}