Completed day 4

day4/Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+[[package]]
+name = "day4"
+version = "0.1.0"
+

day4/Cargo.toml

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+[package]
+name = "day4"
+version = "0.1.0"
+authors = ["Tyler Hallada <tyler@hallada.net>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

day4/src/main.rs

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+const INPUT_MIN: u32 = 245318;
+const INPUT_MAX: u32 = 765747;
+
+fn solve_part1() -> u32 {
+    let mut counter = 0;
+    for num in INPUT_MIN..=INPUT_MAX {
+        let num_string = num.to_string();
+        let mut previous = None;
+        let mut has_double = false;
+        let mut decreasing = false;
+        for c in num_string.chars() {
+            match previous {
+                None => previous = Some(c),
+                Some(p) => {
+                    if p == c {
+                        has_double = true;
+                    }
+                    if p.to_digit(10) > c.to_digit(10) {
+                        decreasing = true;
+                        break;
+                    }
+                    previous = Some(c);
+                }
+            }
+        }
+        if has_double && !decreasing {
+            counter += 1;
+        }
+    }
+    counter
+}
+
+fn solve_part2() -> u32 {
+    // too lazy to DRY it up
+    let mut counter = 0;
+    for num in INPUT_MIN..=INPUT_MAX {
+        let num_string = num.to_string();
+        let mut previous = None;
+        let mut has_double = false;
+        let mut matching_group_count = 1;
+        let mut decreasing = false;
+        for c in num_string.chars() {
+            match previous {
+                None => previous = Some(c),
+                Some(p) => {
+                    if p == c {
+                        matching_group_count += 1;
+                    } else {
+                        if matching_group_count == 2 {
+                            has_double = true;
+                        }
+                        matching_group_count = 1;
+                    }
+                    if p.to_digit(10) > c.to_digit(10) {
+                        decreasing = true;
+                        break;
+                    }
+                    previous = Some(c);
+                }
+            }
+        }
+        if (matching_group_count == 2 || has_double) && !decreasing {
+            counter += 1;
+        }
+    }
+    counter
+}
+
+fn main() {
+    println!("Part 1: {}", solve_part1());
+    println!("Part 2: {}", solve_part2());
+}