1 files changed, 99 insertions, 0 deletions
diff --git a/2017/src/bin/day_8.rs b/2017/src/bin/day_8.rs
new file mode 100644
index 0000000..0359747
--- /dev/null
+++ b/2017/src/bin/day_8.rs
@@ -0,0 +1,99 @@
+extern crate advent_of_code_2017;
+use advent_of_code_2017::*;
+
+extern crate regex;
+use regex::Regex;
+
+#[macro_use]
+extern crate lazy_static;
+
+use std::str::FromStr;
+use std::collections::HashMap;
+use std::cmp;
+
+fn main() {
+    let args = AdventArgs::init();
+    
+    let instructions: Vec<Instruction> = args.input.iter()
+        .map(|line| line.parse().unwrap())
+        .collect();
+    
+    let mut memory: HashMap<String, i32> = HashMap::new();
+    let mut max_mem_ever = 0;
+    
+    for instruction in instructions {
+        if instruction.is_true(&memory) {
+            instruction.execute(&mut memory);
+            max_mem_ever = cmp::max(max_mem_ever, memory.values().max().cloned().unwrap_or(0));
+        }
+    }
+
+    let max_mem = memory.values().max().cloned().unwrap_or(0);
+
+    if args.part == 1 {
+        println!("Highest value in memory is {}", max_mem);
+    } else {
+        println!("Highest value in memory ever is {}", max_mem_ever);
+    }
+}
+
+
+struct Instruction {
+    target_register: String,
+    action: String,
+    value: i32,
+    condition_register: String,
+    condition: String,
+    condition_value: i32
+}
+
+#[derive(Debug)]
+struct InstructionParseError {
+    reason: String
+}
+
+impl FromStr for Instruction {
+    type Err = InstructionParseError;
+    fn from_str(s: &str) -> Result<Self, InstructionParseError> {
+        lazy_static!{
+            static ref INSTRUCTION_RE: Regex = Regex::new(r"^(\w+) (inc|dec) (-?\d+) if (\w+) (<|>|<=|>=|==|!=) (-?\d+)").unwrap();
+        }
+        match INSTRUCTION_RE.captures(s) {
+            Some(caps) => Ok(Instruction{
+                target_register: caps[1].to_string(),
+                action: caps[2].to_string(),
+                value: caps[3].parse().unwrap(),
+                condition_register: caps[4].to_string(),
+                condition: caps[5].to_string(),
+                condition_value: caps[6].parse().unwrap()
+            }),
+            None => Err(InstructionParseError {
+                reason: format!("{} did not match regex", s)
+            })
+        }        
+    }
+}
+
+impl Instruction {
+    fn is_true(&self, memory: &HashMap<String, i32>) -> bool {
+        let mem = memory.get(&self.condition_register).cloned().unwrap_or(0);
+        match self.condition.as_ref() {
+            "<" => mem < self.condition_value,
+            ">" => mem > self.condition_value,
+            "<=" => mem <= self.condition_value,
+            ">=" => mem >= self.condition_value,
+            "==" => mem == self.condition_value,
+            "!=" => mem != self.condition_value,
+            _ => panic!("Unknown condition: {}", self.condition)
+        }
+    }
+
+    fn execute(&self, memory: &mut HashMap<String, i32>) {
+        let modifier = if self.action == "inc" {
+            self.value
+        } else {
+            -self.value
+        };
+        *memory.entry(self.target_register.clone()).or_insert(0) += modifier;
+    }
+}