剑指offer - 把数字翻译成字符串 - JavaScript

// ac地址： https://leetcode-cn.com/problems/ba-shu-zi-fan-yi-cheng-zi-fu-chuan-lcof/
// 原文地址：https://xxoo521.com/2020-03-10-num-to-str/

/**
 * @param {number} num
 * @return {number}
 */
var translateNum = function(num) {
    let result = 0;
    traceback(num + "", 0);
    return result;

    /**
     * @param {string} str
     * @param {number} start
     */
    function traceback(str, start) {
        if (start >= str.length) {
            ++result;
            return;
        }

        traceback(str, start + 1);
        const sub = str.substr(start, 2);
        if (sub.length === 2 && sub >= "10" && sub <= "25") {
            traceback(str, start + 2);
        }
    }
};