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tweak the bigint

This commit is contained in:
Joe Ardent 2022-10-29 13:37:04 -07:00
parent e3de039c39
commit 0ed2722260
1 changed files with 62 additions and 54 deletions
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58
multiply_strings/src/main.rs
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@ -1,20 +1,25 @@
struct S();
impl S {
pub fn multiply(num1: String, num2: String) -> String {
//
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) };
if l1 == 0 || l2 == 0 {
return "0".to_string();
}
let tsize = l1.max(l2);
let mut out: Vec<u32> = (0..(num1.len() + num2.len()))
.into_iter()
.map(|_| 0)
.collect();
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<u32> = (0..i2).into_iter().map(|_| 0).collect();
tmp.reserve(tsize - i2);
let d2 = d2.to_digit(10).unwrap();
for d1 in num1.chars().rev() {
let d1 = d1.to_digit(10).unwrap();
@ -26,21 +31,22 @@ pub fn multiply(num1: String, num2: String) -> String {
if mcarry > 0 {
tmp.push(mcarry);
}
merge(&mut out, &tmp);
}
while let Some(last) = out.last() {
if *last == 0 {
let len = out.len() - 1;
out = out[0..len].to_vec();
} else {
break;
}
}
if out.is_empty() {
out.push(0);
Self::merge(&mut out, &tmp);
}
out.iter().rev().map(|d| d.to_string()).collect()
let s: String = out
.into_iter()
.rev()
.skip_while(|d| *d == 0)
// SAFETY: the input is guaranteed to be valid
.map(|d| unsafe { char::from_digit(d, 10).unwrap_unchecked() })
.collect();
if s.is_empty() {
"0".to_string()
} else {
s
}
}
fn merge(out: &mut [u32], rhs: &[u32]) {
@ -55,19 +61,21 @@ fn merge(out: &mut [u32], rhs: &[u32]) {
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(
dbg!(S::multiply("2".to_string(), "4".to_string()));
dbg!(S::multiply("27".to_string(), "49".to_string()));
dbg!(S::multiply(
"20000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
.to_string(),
"4000000000000000000000000000000000000000000000000000000000000000".to_string()
));
dbg!(multiply("0".to_string(), "8".to_string()));
dbg!(S::multiply("".to_string(), "88".to_string()));
}