43. Multiply Strings

Problem

Given two non-negative integers num1 and num2 represented as strings, return the product of num1 and num2, also represented as a string.

Example 1:

Input: num1 = "2", num2 = "3" Output: "6" 

Example 2:

Input: num1 = "123", num2 = "456" Output: "56088" 

Note:

• The length of both num1 and num2 is < 110.
• Both num1 and num2 contain only digits 0-9.
• Both num1 and num2 do not contain any leading zero, except the number 0 itself.
• You must not use any built-in BigInteger library or convert the inputs to integer directly.

Solution

/** * @param {string} num1 * @param {string} num2 * @return {string} */ var multiply = function(num1, num2) { var len1 = num1.length; var len2 = num2.length; var res = Array(len1 + len2).fill(0); var carry = 0; var val = 0; var index = 0; for (var i = len1 - 1; i >= 0; i--) { carry = 0; for (var j = len2 - 1; j >= 0; j--) { index = len1 + len2 - 2 - i - j; val= (num1[i] * num2[j]) + carry + res[index]; carry = Math.floor(val / 10); res[index] = val % 10; } if (carry) res[index + 1] = carry; } while (res.length > 1 && res[res.length - 1] === 0) res.pop(); return res.reverse().join(''); }; 

Explain:

nope.

Complexity:

• Time complexity : O(m*n).
• Space complexity : O(log(m*n)).