整数转换英文表示

将非负整数 num 转换为其对应的英文表示。

  • 输入：num = 123

  • 输出：”One Hundred Twenty Three”

  • 输入：num = 12345

  • 输出：”Twelve Thousand Three Hundred Forty Five”

  • 输入：num = 1234567

  • 输出：”One Million Two Hundred Thirty Four Thousand Five Hundred Sixty Seven”

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// 朴素
var numberToWords = function(num) {
    if (!num) return 'Zero';
    const numMap = {1: 'One', 2: 'Two', 3: 'Three', 4: 'Four', 5: 'Five', 6: 'Six', 7: 'Seven', 8: 'Eight', 9: 'Nine', 10: 'Ten', 11: 'Eleven', 12: 'Twelve', 13: 'Thirteen', 14: 'Fourteen', 15: 'Fifteen', 16: 'Sixteen', 17: 'Seventeen', 18: 'Eighteen', 19: 'Nineteen', 20: 'Twenty', 30: 'Thirty', 40: 'Forty', 50: 'Fifty', 60: 'Sixty', 70: 'Seventy', 80: 'Eighty', 90: 'Ninety'};
    const pointMap = {0: '', 1: 'Thousand', 2: 'Million', 3: 'Billion'};

    const arr = [];
    let restNum = num;
    for(let i = 0; i <= 3; i++) {
        const mod = restNum % 1000;
        restNum = Math.floor(restNum / 1000);
        arr.unshift(mod);
        if (!restNum) break;
    }
    const readItem = (num) => {
        let str = [];
        const h = Math.floor(num / 100);
        mod = num % 100;
        if (h > 0) {
            str.push(numMap[h] + ' Hundred');
        }
        if (mod) {
            if (mod <= 20) {
                str.push(numMap[mod]);
            } else {
                const p1 = mod - (mod % 10);
                str.push(numMap[p1]);
                if (mod % 10) {
                    str.push(numMap[mod % 10]);
                }
            }
        }
        return str.join(' ');
    }

    const readAll = (stack, idx, temp) => {
        if (!stack.length) {
            return temp.filter(i => i).join(' ');
        }
        let cur = readItem(stack.pop());
        cur = cur ? cur + `${idx > 0 ? ' ' + pointMap[idx] : ''}` : '';
        return readAll(stack, idx+1, [cur, ...temp]);
    }

    return readAll(arr, 0, []);
};