function reverse(input) {
    if (!input) {
        return [];
    }

    if (input.length <= 1) {
        return [...input];
    }

    let start = 0;
    let end = 0;

    const result = [];

    for (let i = 1; i < input.length; i++) {
        if (isWordLetter(input[i])) {
            end++;
            continue;
        }

        for (let j = end; j >= start; j--) {
            result.push(input[j]);
        }

        while(input[i] && !isWordLetter(input[i])) {
            result.push(input[i]);
            i++;
        }

        start = i;
        end = i;
    }

    if (result.length < input.length) {
        let index = end;
        while (index >= start) {
            result.push(input[index]);
            index--;
        }
    }

    return result;
}

function isWordLetter(symbol) {
    return isLowercaseLetter(symbol) || isUppercaseLetter(symbol) || isNumber(symbol);
}

function isLowercaseLetter(symbol) {
    const code = symbol.charCodeAt(0);

    return code >= 97 && code <= 122;
}

function isUppercaseLetter(symbol) {
    const code = symbol.charCodeAt(0);

    return code >= 65 && code <= 90;
}

function isNumber(symbol) {
    const code = symbol.charCodeAt(0);

    return code >= 48 && code <= 57;
}

console.log('a:', 'a'.charCodeAt(0));
console.log('z:', 'z'.charCodeAt(0));
console.log('A:', 'A'.charCodeAt(0));
console.log('Z:', 'Z'.charCodeAt(0));
console.log('0:', '0'.charCodeAt(0));
console.log('9:', '9'.charCodeAt(0));

const demoInput = ['I',' ', ' ', ' ', 'L','o','v','e',' ',' ',' ','N','u','O','R','D','E','R','!'];
console.log('demoInput:', reverse(demoInput));

const singleWordInput = ['N','u','O','R','D','E','R','N','u','O','R','D','E','R'];
console.log('singleWordInput:', reverse(singleWordInput));

const whitespacesInput = [' ','"',' ', '@',' ','!'];
console.log('whitespacesInput:', reverse(whitespacesInput));

console.log('no input', reverse());

const singleLetterInput = ['a'];
console.log('singleLetterInput', reverse(singleLetterInput));