除法

其實就是借位相減。

a='157794750267131502212476817800345498121872783333389747424011531025366277535262539913701806290766479189477533597854989606803194253978660329941980786072432806427833685472618792592200595694346872951301770580765135349259590167490536138082469680638514416594216629258349130257685001248172188325316586707301643237607'
b='65'

x = a.split('').map(e => parseInt(e))
y = b.split('').map(e => parseInt(e))

div(x, y)

const div = (x, y) => {
    const
        q = []

    let
        cmp, times,
        next = y.length,
        r = x.slice(0, y.length)

    do {
        for (times = 0; times < 10; times++) {
            /*
            * 比較除數與余數大小
            * 除數 > 余數 ? 1 : -1
            */
            if (y.length != r.length)
                cmp = y.length > r.length ? 1 : -1
            else {
                cmp = 0
                for (let i = 0; i < r.length; i++) {
                    if (y[i] != r[i]) {
                        cmp = y[i] > r[i] ? 1 : -1
                        break
                    }
                }
            }

            /*
            * 余數大于除數
            * 余數減去除數
            */
            if (cmp < 0) {
                const
                    delta = r.length - y.length
                let
                    _i,
                    carry = 0

                for (let i = y.length - 1; i >= 0; i--) {
                    _i = i + delta
                    r[_i] = r[_i] - y[i] + carry
                    r[_i] < 0 ? (r[_i] += 10, carry = -1) : carry = 0
                }
                carry && (r[_i-1] += carry)
                for (; !r[0]; r.shift()) {}
            } else break
        }
        q[next] = cmp ? times : (r = [x[next]], ++times)
        cmp == 1 && r.push(x[next])
    } while (next++ < x.length)
    return q
}