From 8a60920998efe8cdb8c1c98e8669e366affd695e Mon Sep 17 00:00:00 2001
From: Joe Ardent <code@ardent.nebcorp.com>
Date: Fri, 28 Oct 2022 17:10:36 -0700
Subject: [PATCH] bigint for strings works with my compiler, but not leetcode's

---
 multiply_strings/Cargo.toml  |  8 +++++
 multiply_strings/src/main.rs | 67 ++++++++++++++++++++++++++++++++++++
 2 files changed, 75 insertions(+)
 create mode 100644 multiply_strings/Cargo.toml
 create mode 100644 multiply_strings/src/main.rs

diff --git a/multiply_strings/Cargo.toml b/multiply_strings/Cargo.toml
new file mode 100644
index 0000000..756474d
--- /dev/null
+++ b/multiply_strings/Cargo.toml
@@ -0,0 +1,8 @@
+[package]
+name = "multiply_strings"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
diff --git a/multiply_strings/src/main.rs b/multiply_strings/src/main.rs
new file mode 100644
index 0000000..57356ca
--- /dev/null
+++ b/multiply_strings/src/main.rs
@@ -0,0 +1,67 @@
+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()
+    ));
+}