43. Multiply Strings Medium

1/**
2 * [43] Multiply Strings
3 *
4 * Given two non-negative integers num1 and num2 represented as strings, return the product of num1 and num2, also represented as a string.
5 * Note: You must not use any built-in BigInteger library or convert the inputs to integer directly.
6 *  
7 * Example 1:
8 * Input: num1 = "2", num2 = "3"
9 * Output: "6"
10 * Example 2:
11 * Input: num1 = "123", num2 = "456"
12 * Output: "56088"
13 *  
14 * Constraints:
15 *
16 * 1 <= num1.length, num2.length <= 200
17 * num1 and num2 consist of digits only.
18 * Both num1 and num2 do not contain any leading zero, except the number 0 itself.
19 *
20 */
21pub struct Solution {}
22
23// problem: https://leetcode.com/problems/multiply-strings/
24// discuss: https://leetcode.com/problems/multiply-strings/discuss/?currentPage=1&orderBy=most_votes&query=
25
26// submission codes start here
27
28impl Solution {
29    pub fn multiply(num1: String, num2: String) -> String {
30        let mut r: Vec<i32> = vec![0; num1.len() + num2.len()];
31        for (i, v1) in num1.chars().rev().enumerate() {
32            for (j, v2) in num2.chars().rev().enumerate() {
33                let got = (v1 as i32 - '0' as i32) * (v2 as i32 - '0' as i32);
34                let n = got + r[i + j];
35                r[i + j] = n % 10;
36                r[i + j + 1] += n / 10;
37            }
38        }
39        let mut result = String::new();
40        for i in r.into_iter().rev() {
41            if result.is_empty() && i == 0 {
42                continue;
43            } else {
44                result.push(char::from_digit(i as u32, 10).unwrap());
45            }
46        }
47        if result.is_empty() {
48            String::from("0")
49        } else {
50            result
51        }
52    }
53}
54
55// submission codes end
56
57#[cfg(test)]
58mod tests {
59    use super::*;
60
61    #[test]
62    fn test_43() {
63        assert_eq!(
64            "56088".to_owned(),
65            Solution::multiply("123".to_string(), "456".to_string())
66        );
67    }
68}
69