get total count of specific digit(0~9) from 1 to number

README.md

get total count of specific digit(0~9) from 1 to number

https://www.acmicpc.net/problem/14912

Example

> getDigitTotal(10, 1)
> 2
// 1 = 1
// 2 = 0
// ...
// 10 = 1

> getDigitTotal(11, 1)
> 4
// 1 = 1
// 2 = 0
// ...
// 10 = 1
// 11 = 2

getDigitTotal1.js

function getDigitTotal(num, digit) {
    const regex = new RegExp(`${digit}`, "g");
    let sum = 0;
    for (i = 1; i <= num; i++) {
        const count = (`${i}`.match(regex)||[]).length;
        sum += count;
    }
    return sum;
}

tc.js

function tc() {
    [
        { num: 1,    digit: 1, result: 1 },
        { num: 2,    digit: 1, result: 1 },
        { num: 3,    digit: 1, result: 1 },
        { num: 4,    digit: 1, result: 1 },
        { num: 5,    digit: 1, result: 1 },
        { num: 9,    digit: 1, result: 1 },
        { num: 10,   digit: 1, result: 2 },
        { num: 20,   digit: 1, result: 12 },
        { num: 22,   digit: 1, result: 13 },
        { num: 22,   digit: 2, result: 6 },
        { num: 70,   digit: 1, result: 17 },
        { num: 70,   digit: 6, result: 17 },
        { num: 70,   digit: 7, result: 8 },
        { num: 1000, digit: 1, result: 301 },
        { num: 2000, digit: 1, result: 1600 },
    ].forEach(({num, digit, result}) => {
        const actual = getDigitTotal(num, digit);
        const isSuccess = actual === result;
        const logMessage = `expect: ${result}, actual: ${actual} (num: ${num}, digit: ${digit})`

        isSuccess ? console.log(logMessage) : console.error(logMessage)
    })
}

 // 0 ~ 9
Math.floor(num % 10) >= digit ? 1 : 0 // units
// 0 ~ 99
(Math.floor(num / 10) + (Math.floor(num / 10) > digit ? 10 : 0)) // tens
+ (Math.floor(num % 10) >= digit ? 1 : 0); // units
// hundreds(100)
// thousands(1000)
// ten thousands(10000)
// hundred thousands(100000)
// millions(1000000)