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Big Integer multiplication.java
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Big Integer multiplication.java
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/*
Description
Given two non-negative integers num1 and num2 represented as strings, return the product of num1 and num2
Example
The length of both num1 and num2 is < 110.
Both num1 and num2 contains only digits 0-9.
Both num1 and num2 does not contain any leading zero.
You must not use any built-in BigInteger library or convert the inputs to integer directly.
Tags
String Mathematics Twitter Facebook
*/
/**
* This Question is the same as Multiply String in LeetCode
* You can get more explanations here:
* https://github.com/cherryljr/LeetCode/blob/master/Multiply%20Strings.java
*/
public class Solution {
/*
* @param num1: a non-negative integers
* @param num2: a non-negative integers
* @return: return product of num1 and num2
*/
public String multiply(String num1, String num2) {
int[] pos = new int[num1.length() + num2.length()];
// Calculate the result of each index in the pos array.
for (int i = num1.length() - 1; i >= 0; i--) {
for (int j = num2.length() - 1; j >= 0; j--) {
int p1 = i + j, p2 = i + j + 1;
int mul = (num1.charAt(i) - '0') * (num2.charAt(j) - '0');
// The current sum equals mul plus the ten's digit from the last mul
// (pos[p2], or you can find from the draft directly, they are in the same column)
int sum = mul + pos[p2];
pos[p1] += sum / 10;
pos[p2] = sum % 10;
}
}
// Turn the pos array into String result
StringBuilder sb = new StringBuilder();
for (int p : pos) {
if (!(sb.length() == 0 && p == 0)) {
sb.append(p);
}
}
return sb.length() == 0 ? "0" : sb.toString();
}
}