/**
 * Time O(N) | Space O(N)
 * https://leetcode.com/problems/plus-one/
 * @param {number[]} digits
 * @return {number[]}
 */
var plusOne = (digits) => {
    add(digits);
    carry(digits); /* Time O(N) */
    addLeading(digits); /*           | Space O(N) */

    return digits;
};

var add = (digits) => (digits[digits.length - 1] += 1);

var carry = (digits) => {
    for (let digit = digits.length - 1; 0 < digit; digit--) {
        /* Time O(N) */
        const canCarry = digits[digit] === 10;
        if (!canCarry) break;

        digits[digit] = 0;
        digits[digit - 1] += 1;
    }
};

const addLeading = (digits) => {
    const canCarry = digits[0] === 10;
    if (!canCarry) return;

    digits[0] = 1;
    digits.push(0); /* Space O(N) */
};

/**
 * Time O(N) | Space O(N)
 * https://leetcode.com/problems/plus-one/
 * @param {number[]} digits
 * @return {number[]}
 */
var plusOne = (digits) => {
    for (let digit = digits.length - 1; 0 <= digit; digit--) {
        /* Time O(N) */
        const canCarry = digits[digit] === 9;
        if (canCarry) {
            digits[digit] = 0;
            continue;
        }

        digits[digit]++;

        return digits;
    }

    digits.unshift(1); /* Time O(N) | Space O(N) */

    return digits;
};

/**
 * Time O(N) | Space O(N)
 * https://leetcode.com/problems/plus-one/
 * @param {number[]} digits
 * @return {number[]}
 */
var plusOne = function (digits) {
    var i = digits.length - 1;

    while (digits[i] + 1 === 10) {
        digits[i] = 0;
        i -= 1;
    }

    if (i < 0) {
        digits.unshift(1);
    } else {
        digits[i] += 1;
    }

    return digits;
};