# Javascript solution using sum of characters

• ``````var findTheDifference = function(s, t) {
if (s.length === 0) return t;
var letters = 'abcdefghijklmnopqrstuvwxyz';
var sSum = s.split('').map(e => e.charCodeAt(0) - 'a'.charCodeAt(0)).reduce((a, b) => a + b);
var tSum = t.split('').map(e => e.charCodeAt(0) - 'a'.charCodeAt(0)).reduce((a, b) => a + b);
return letters[tSum -sSum];
};
``````

• You can use xor operation but you need to convert character to it's unicode value and back to character.

``````function findTheDifference(s, t) {
//convert char to num, since xor operator will cast char to num
let c = t.charCodeAt(t.length-1);
for(let i=0; i < s.length; i++){
c = c ^ s.charCodeAt(i) ^ t.charCodeAt(i);
}
return String.fromCharCode(c);
};

``````

• ``````var findTheDifference = function(s, t) {
var l = s.length;
var c = t.charCodeAt(s.length);
for (var i=0; i<l; i+=1){
c -= s.charCodeAt(i);
c += t.charCodeAt(i);
}
return String.fromCharCode(c);
};
``````

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