Algorithm: format thousands of digits

topic

Format thousands of digits, for example:
10201004050 is converted to 10,201,004,050

train of thought

Note that it is a reverse order judgment, and a comma is added for every 3 digits.

Idea 1: Convert to an array, perform reverse traversal, and split every 3 digits
Idea 2: Convert to a string, traverse in reverse order, and split every 3 digits
Idea 3: Regular (poor performance)

Performance:
number > string > array > regular

the code

/**
 * 千分位格式化（使用数组）
 * @param n number
 */
export function format1(n: number): string {
    
    
    n = Math.floor(n) // 只考虑整数

    const s = n.toString()
    const arr = s.split('').reverse()
    return arr.reduce((prev, val, index) => {
    
    
        if (index % 3 === 0) {
    
    
            if (prev) {
    
    
                return val + ',' + prev
            } else {
    
    
                return val
            }
        } else {
    
    
            return val + prev
        }
    }, '')
}

/**
 * 数字千分位格式化（字符串分析）
 * @param n number
 */
export function format2(n: number): string {
    
    
    n = Math.floor(n) // 只考虑整数

    let res = ''
    const s = n.toString()
    const length = s.length

    for (let i = length - 1; i >= 0; i--) {
    
    
        const j = length - i
        if (j % 3 === 0) {
    
    
            if (i === 0) {
    
    
                res = s[i] + res
            } else {
    
    
                res = ',' + s[i] + res
            }
        } else {
    
    
            res = s[i] + res
        }
    }

    return res
}

// 功能测试
const n = 10201004050
console.info('format1', format1(n))
console.info('format2', format2(n))