JS
function findMissingLetter(array) {
for (let i = 0; i < array.length; i++) {
if (array[i].charCodeAt(0) !== (array[i+1].charCodeAt(0) - 1)) {
console.log(array[i].charCodeAt(0), array[i+1].charCodeAt(0))
return String.fromCharCode(array[i+1].charCodeAt(0) - 1)
}
}
}