Finish part 2 of puzzle 5 for 2015.

2015/puzzle-5.rs

@@ -1,27 +1,29 @@
 use std::fs;
 
+const VOWELS_STR: &str = "aeiou";
+const DO_NOT_WANT: [&str; 4] = ["ab", "cd", "pq", "xy"];
+
 fn is_nice_round1(line: &str) -> bool {
-    let do_not_want: [&str; 4] = ["ab", "cd", "pq", "xy"];
     let mut unwanted_substr = false;
     let mut has_consecutive = false;
     let mut vowels = 0;
     for i in 0..line.len() - 1 {
-        let substr: &str = &line[i..i + 2];
-        if do_not_want.iter().position(|&x| x == substr).is_some() {
+        let slide: &str = &line[i..i + 2];
+        if DO_NOT_WANT.iter().position(|&x| x == slide).is_some() {
             unwanted_substr = true;
             break;
         }
-
-        if "aeiou".contains(substr.chars().nth(0).unwrap()) {
+        let first = slide.chars().nth(0).unwrap();
+        let second = slide.chars().nth(1).unwrap();
+        if VOWELS_STR.contains(first) {
             vowels += 1;
         }
-
-        if substr.chars().nth(0).unwrap() == substr.chars().nth(1).unwrap() {
+        if first == second {
             has_consecutive = true;
         }
     }
 
-    if "aeiou".contains(line.chars().nth(line.len() - 1).unwrap()) {
+    if VOWELS_STR.contains(line.chars().nth(line.len() - 1).unwrap()) {
         vowels += 1;
     }
 
@@ -31,11 +33,46 @@ fn is_nice_round1(line: &str) -> bool {
     return vowels >= 3 && has_consecutive;
 }
 
+fn is_nice_round2(line: &str) -> bool {
+    /*
+    Justifying the O(|line|^2) runtime is easy: |line| is constant, such that at
+    worst we're doing roughly O(256) iterations.  Not too bad.
+
+    If |line| could be really big I'd look into optimising the rest, but why do
+    that?
+     */
+    let mut has_pair = false;
+
+    // Unfortunate O(|line|^2) runtime
+    for i in 0..line.len() - 1 {
+        let slide = &line[i..i + 2];
+        let rest = &line[i + 2..];
+        if rest.contains(slide) {
+            has_pair = true;
+            break;
+        }
+    }
+
+    // O(|line|) runtime
+    let mut has_triple = false;
+    for i in 0..line.len() - 2 {
+        let slide = &line[i..i + 3];
+        if slide.chars().nth(0) == slide.chars().nth(2) {
+            has_triple = true;
+            break;
+        }
+    }
+
+    return has_pair && has_triple;
+}
+
 fn main() {
     let binding = fs::read_to_string("5-input").expect("wget 5-input please.");
     let contents: Vec<&str> = binding.split("\n").collect();
     let nice_lines_1 = contents.iter().filter(|&x| is_nice_round1(x)).count();
+    let nice_lines_2 = contents.iter().filter(|&x| is_nice_round2(x)).count();
     println!("Round 1: {nice_lines_1}");
+    println!("Round 2: {nice_lines_2}");
 }
 
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