/**
*
* 大数乘法 模拟乘法
*
* @param {string} num1 整数字符串
* @param {string} num2 整数字符串
* @return {string} 整数字符串
*/
function multiplication(num1, num2) {
const result = Array.from({ length: num1.length + num2.length }, () => 0);
const len1 = num1.length;
const len2 = num2.length;
for (let i = len1 - 1; i >= 0; i -= 1) {
let carry = 0;
for (let j = len2 - 1; j >= 0; j -= 1) {
result[i + j + 1] += carry + num1[i] * num2[j];
carry = Math.floor(result[i + j + 1] / 10);
result[i + j + 1] = result[i + j + 1] % 10;
}
result[i] += carry;
}
return result.join('').replace(/^0+(\d)/, '$1');
}