Untitled

import {last} from "lodash";

export function subtract(a: string, b: string) : string {
    const A = a.split('');
    const B = b.split('');
    const result = [];
    let carryOnNumber = 0;
    while (A.length > 0 || B.length > 0) {
 
		const lastDigitA = A.pop();
        const lastDigitB = B.pop();
        const subtraction = parseInt(lastDigitA ?? "0") - parseInt(lastDigitB ?? "0") - carryOnNumber;
   
        carryOnNumber = subtraction < 0 ? 1 : 0;

        if (subtraction == 0) {
            if (A.length > 0) {
                result.push(0);
            } else if (result.length == 0) {
                result.push(0);
            }
        } else {
            result.push( (10 + subtraction)%10 );
            if (A.length == 0 && (B.length > 0 || carryOnNumber)) {
                // B > A and we need to show negative sign
                result.push("-");
            }
        }
    }
    while (result.length > 1 && result.slice(-1)[0] == 0) {
        result.pop();
    }
    return result.reverse().join('');
}

const tests = [
    ["123123123", "34342343"],
    ["100000", "0"],
    ["123", "123"],
    ["6", "6"],
    ["1000","1"],
    ["10000", "100"]
];

tests.forEach(x => {
    const correctAnswer = (parseInt(x[0]) - parseInt(x[1])).toString();
    console.log(x, correctAnswer, subtract(x[0], x[1]), correctAnswer == subtract(x[0], x[1]))
})