剑指Offer——1~n整数中1出现的次数（JS实现）

var countDigitOne = function(n) {
    let flag = 0;
    const TotalBase = Math.pow(10,(String(n).split('').length) - 1);
    for (let i = 0; Math.pow(10,i) <= TotalBase; i++) {
        let base = Math.pow(10,i);
        let cur = Math.floor(n/base) % 10;
        let a = Math.floor(Math.floor(n/base) / 10);
        let b = n % base;
        if (cur < 1) {
            flag = flag + a * base;
        } else if (cur > 1) {
            flag = flag + (a + 1) * base;
        } else {
            flag = flag + a * base + b + 1;
        }
    }
    return flag;
};