From e1e03896d5a61d5c311a92b29c6d50640df1015c Mon Sep 17 00:00:00 2001
From: Ishan Jain <contact@ishanjain.me>
Date: Fri, 1 Dec 2023 15:04:54 +0530
Subject: [PATCH] optimized day1

---
 src/day1/2.rs | 97 ++++++++++++++++++++++++++++-----------------------
 1 file changed, 53 insertions(+), 44 deletions(-)

diff --git a/src/day1/2.rs b/src/day1/2.rs
index e8d3c9e..2b308b8 100644
--- a/src/day1/2.rs
+++ b/src/day1/2.rs
@@ -7,51 +7,10 @@ fn process(data: &str) -> u64 {
     let mut total: u64 = 0;
 
     for line in data.split('\n') {
-        let mut first = 0;
-        let mut last = 0;
+        let line: Vec<char> = line.chars().collect();
 
-        let mut window = Vec::with_capacity(line.len());
-        let mut j = 0;
-
-        for (i, c) in line.chars().enumerate() {
-            if (window.len() - j) >= 5 {
-                j += 1;
-            }
-
-            match c {
-                v @ '1'..='9' if first == 0 => {
-                    let num = v as u8 - b'0';
-                    first = 10 * num;
-                    last = num;
-
-                    j = i + 1;
-                }
-                v @ '1'..='9' => {
-                    let num = v as u8 - b'0';
-                    last = num;
-
-                    j = i + 1;
-                }
-                _ => (),
-            }
-            window.push(c);
-
-            if window.len() - j >= 3 {
-                if let Some(digit) = get_digit(&window[j..]) {
-                    if first == 0 {
-                        first = 10 * digit;
-                    }
-                    last = digit;
-                }
-            }
-        }
-
-        if let Some(digit) = get_digit(&window[j..]) {
-            if first == 0 {
-                first = 10 * digit;
-            }
-            last = digit;
-        }
+        let first = 10 * find_forward(&line);
+        let last = find_backward(&line);
 
         total += first as u64 + last as u64;
     }
@@ -59,6 +18,56 @@ fn process(data: &str) -> u64 {
     total
 }
 
+fn find_forward(iter: &[char]) -> u8 {
+    let mut start = 0;
+    let mut end = 0;
+
+    for c in iter.iter() {
+        if ('1'..='9').contains(c) {
+            return *c as u8 - b'0';
+        }
+
+        if end - start >= 5 {
+            start += 1;
+        }
+        end += 1;
+
+        if end - start >= 3 {
+            if let Some(digit) = get_digit(&iter[start..end]) {
+                return digit;
+            }
+        }
+    }
+
+    get_digit(&iter[start..end]).unwrap_or(0)
+}
+fn find_backward(iter: &[char]) -> u8 {
+    if iter.is_empty() {
+        return 0;
+    }
+    let mut start = iter.len() - 1;
+    let mut end = iter.len();
+
+    for c in iter.iter().rev() {
+        if ('1'..='9').contains(c) {
+            return *c as u8 - b'0';
+        }
+        if end - start >= 5 {
+            end -= 1;
+        }
+
+        start -= 1;
+
+        if end - start >= 3 {
+            if let Some(digit) = get_digit(&iter[start..end]) {
+                return digit;
+            }
+        }
+    }
+
+    get_digit(&iter[start..end]).unwrap_or(0)
+}
+
 fn main() {
     for input in INPUTS.iter() {
         println!("total = {}", process(input));