dumb_shit/multiply_strings/src/main.rs

68 lines
1.8 KiB
Rust
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pub fn multiply(num1: String, num2: String) -> String {
//
let mut out: Vec<u32> = Vec::from_iter((0..(num1.len() + num2.len())).into_iter().map(|_| 0));
let l1 = num1.len();
let l2 = num2.len();
// get the longest one as num1
let (num1, num2) = if l1 < l2 { (num2, num1) } else { (num1, num2) };
for (i2, d2) in num2.chars().rev().enumerate() {
let mut mcarry = 0;
let mut tmp = Vec::from_iter((0..i2).into_iter().map(|_| 0));
let d2 = d2.to_digit(10).unwrap();
for d1 in num1.chars().rev() {
let d1 = d1.to_digit(10).unwrap();
let p = (d1 * d2) + mcarry;
mcarry = p / 10;
let p = p % 10;
tmp.push(p);
}
if mcarry > 0 {
tmp.push(mcarry);
}
merge(&mut out, &tmp);
}
let out = if let Some(last) = out.last() {
if *last == 0 {
let len = out.len() - 1;
&out[0..len]
} else {
&out[0..]
}
} else {
&out[0..]
};
out.iter().rev().map(|d| d.to_string()).collect()
}
fn merge(out: &mut [u32], rhs: &[u32]) {
//
let mut acarry = 0;
let len = rhs.len();
(0..len).for_each(|i| {
let oi = out[i];
let ri = rhs[i];
let s = oi + ri + acarry;
acarry = s / 10;
let s = s % 10;
out[i] = s;
});
if acarry > 0 {
out[len] = acarry;
}
}
fn main() {
dbg!(multiply("2".to_string(), "4".to_string()));
dbg!(multiply("27".to_string(), "49".to_string()));
dbg!(multiply(
"20000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
.to_string(),
"4000000000000000000000000000000000000000000000000000000000000000".to_string()
));
}