I was doing following leetcode question on multiplying
Given two non-negative integers num1 and num2 represented as strings, return the
product of num1 and num2, also represented as a string.
Note: You must not use any built-in BigInteger library or convert the inputs to
integer directly.
Example 1:
Input: num1 = "2", num2 = "3"
Output: "6"
Example 2:
Input: num1 = "123", num2 = "456"
Output: "56088"
Constraints:
- 1 <= num1.length, num2.length <= 200
- num1 and num2 consist of digits only.
- Both num1 and num2 do not contain any leading zero, except the number 0 itself.
For this used the following approach
Algo for the same is
const numberMap = {
"0": 0,
"1": 1,
"2": 2,
"3": 3,
"4": 4,
"5": 5,
"6": 6,
"7": 7,
"8": 8,
"9": 9
}
var multiply = function(num1, num2) {
let i = num1.length
let j = num2.length
let sum = currentPower = 0
let firstNumber = secondNumber = 0
while(i > 0 || j > 0) {
// if I or J is equal to zero, means we have iterated hence we will set the value to one
const firstNum = i > 0 ? (numberMap[num1[i-1]]) * (10**currentPower) : 0
const secondNum = j > 0 ? (numberMap[num2[j-1]]) * (10**currentPower) : 0
firstNumber += firstNum
secondNumber += secondNum
currentPower++
i--
j--
}
sum = firstNumber * secondNumber
return sum.toString()
};
but when the following input is given
"123456789"
"987654321"
it yields the following output "121932631112635260" instead of "121932631112635269"
Any idea how I can fix this?
You could multiply each digit with each other digit and take the indices as position.
Like you would do by hand, like
1 2 3 4 * 4 3 2 1 ------------------------- 1 2 3 4 1 4 6 8 3 6 9 12 4 8 12 16 ------------------------- 5 3 2 2 1 1 4
This approach uses the reversed arrays of the strings and reverse the result set as well.
Before retuning the result, the array is filterd by the leading zeros.
function multiply(a, b) {
var aa = [...a].reverse(),
bb = [...b].reverse(),
p = [],
i, j;
for (i = 0; i < aa.length; i++) {
for (j = 0; j < bb.length; j++) {
if (!p[i + j]) p[i + j] = 0;
p[i + j] += aa[i] * bb[j];
if (p[i + j] > 9) {
if (!p[i + j + 1]) p[i + j + 1] = 0;
p[i + j + 1] += Math.floor(p[i + j] / 10);
p[i + j] %= 10;
}
}
}
return p
.reverse()
.filter((valid => (v, i, { length }) => valid = +v || valid || i + 1 === length)(false))
.join('');
}
console.log(multiply('2', '3')); // 6
console.log(multiply('123', '456')); // 56088
console.log(multiply('9133', '0')); // 0
console.log(multiply('9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999', '9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999'));