SOURCE

const str = '25525511135'

// 暴力求解
const fn = (str) => {
    let res = []
    for (let i = 0; i < str.length - 3; i++) {
        let p1 = str.substring(0, i + 1)
        if (!isValidate(p1)) {
            continue
        }
        for (let j = i + 1; j < str.length - 2; j++) {
            let p2 = str.substring(i + 1, j + 1)
            if (!isValidate(p2)) {
                continue
            }
            for (let k = j + 1; k < str.length - 1; k++) {
                let p3 = str.substring(j + 1, k + 1)
                let p4 = str.substring(k + 1, str.length)
                if (!isValidate(p3) || !isValidate(p4)) {
                    continue
                }
                res.push(`${p1}.${p2}.${p3}.${p4}`)
            }
        }
    }
    console.log(res)
}
// 验证是否合法
const isValidate = (str) => {
    if (str.length >= 4 || (str.length > 1 && str.charAt(0) === 0) || str > 255) {
        return false
    }
    return true
}

fn(str)