array = ['Siya', 'Drinking', 'Fucking', 'Eating'];

let map = {}
function cv() {
    let result = ""
    array.forEach(element => {
        let v = element.length; // length of every word
        console.log(v)

        // checks and add the last letter of the word
        if(map[element[v - 1]] == undefined) {
            map[element[v - 1]] = 1
        } else {
            let x  = element[v - 1];
            // we get the letter as 'x' the call endWithLetter() with the original array and the repeating letter
            result = endWithLetter(array, x);
        }
    });
    return result;
}


function endWithLetter(array, letter) {
    var newArr = []
    for (let i = 0; i < array.length; i++) {
        const element = array[i];
        // loops through array and push the word that end with the given letter
        if(element.endsWith(letter)) {
            newArr.push(element);
        }
    }
    return newArr;
}

console.log(cv())