3 files changed, 133 insertions, 0 deletions

diff --git a/2022/21/a.rs b/2022/21/a.rs
new file mode 100644
index 0000000..297f97a
--- /dev/null
+++ b/2022/21/a.rs
@@ -0,0 +1,19 @@
+mod common;
+use common::*;
+
+pub fn calculate(name: &str, monkeys: &Vec<Monkey>) -> i64 {
+    let i = monkeys.iter().position(|m| m.name == name).unwrap();
+    match &monkeys[i].kind {
+        MonkeyType::Num(n) => *n,
+        MonkeyType::Op(op) => {
+            let n1 = calculate(&op.m1, &monkeys);
+            let n2 = calculate(&op.m2, &monkeys);
+            apply_op(n1, n2, op)
+        }
+    }
+}
+
+fn main() {
+    let monkeys = read_monkeys_from_stdin();
+    println!("{}", calculate(&"root", &monkeys));
+}
diff --git a/2022/21/b.rs b/2022/21/b.rs
new file mode 100644
index 0000000..e674dd4
--- /dev/null
+++ b/2022/21/b.rs
@@ -0,0 +1,63 @@
+mod common;
+use common::*;
+
+fn solve_for_humn(name: &str, n1: i64, monkeys: &Vec<Monkey>) -> i64 {
+    if name == "humn" { return n1; }
+
+    let i = monkeys.iter().position(|m| m.name == name).unwrap();
+    if let MonkeyType::Op(op) = &monkeys[i].kind {
+        if let Some(n2) = result_or_unknown(&op.m1, &monkeys) {
+            // n1 = n2 [op] [unknown]
+            match op.op {
+                '+' => solve_for_humn(&op.m2, n1-n2, &monkeys),
+                '-' => solve_for_humn(&op.m2, n2-n1, &monkeys),
+                '*' => solve_for_humn(&op.m2, n1/n2, &monkeys),
+                '/' => solve_for_humn(&op.m2, n2/n1, &monkeys),
+                _ => panic!("invalid operator")
+            }
+        } else {
+            if let Some(n2) = result_or_unknown(&op.m2, &monkeys) {
+                // n1 = [unknown] [op] n2
+                match op.op {
+                    '+' => solve_for_humn(&op.m1, n1-n2, &monkeys),
+                    '-' => solve_for_humn(&op.m1, n1+n2, &monkeys),
+                    '*' => solve_for_humn(&op.m1, n1/n2, &monkeys),
+                    '/' => solve_for_humn(&op.m1, n1*n2, &monkeys),
+                    _ => panic!("invalid operator")
+                }
+            } else { panic!("both sides undetermined"); }
+        }
+    } else { panic!("found number when trying to solve for humn"); }
+}
+
+fn result_or_unknown(name: &str, monkeys: &Vec<Monkey>) -> Option<i64> {
+    if name == "humn" { return None; }
+
+    let i = monkeys.iter().position(|m| m.name == name).unwrap();
+    match &monkeys[i].kind {
+        MonkeyType::Num(n) => Some(*n),
+        MonkeyType::Op(op) => {
+            let n1 = result_or_unknown(&op.m1, &monkeys)?;
+            let n2 = result_or_unknown(&op.m2, &monkeys)?;
+            Some(apply_op(n1, n2, op))
+        }
+    }
+}
+
+pub fn solve(monkeys: &Vec<Monkey>) -> i64 {
+    let i = monkeys.iter().position(|m| m.name == "root").unwrap();
+    if let MonkeyType::Op(op) = &monkeys[i].kind {
+        if let Some(n) = result_or_unknown(&op.m1, &monkeys) {
+            return solve_for_humn(&op.m2, n, monkeys);
+        } else {
+            if let Some(n) = result_or_unknown(&op.m2, &monkeys) {
+                return solve_for_humn(&op.m1, n, &monkeys);
+            } else { panic!("humn not found"); }
+        }
+    } else { panic!("root monkey is of type number"); }
+}
+
+fn main() {
+    let monkeys = read_monkeys_from_stdin();
+    println!("{}", solve(&monkeys));
+}
diff --git a/2022/21/common.rs b/2022/21/common.rs
new file mode 100644
index 0000000..24dc37b
--- /dev/null
+++ b/2022/21/common.rs
@@ -0,0 +1,51 @@
+#[derive(Debug)]
+pub struct Operation {
+    pub m1: String,
+    pub m2: String,
+    pub op: char
+}
+
+#[derive(Debug)]
+pub enum MonkeyType {
+    Num(i64),
+    Op(Operation)
+}
+
+#[derive(Debug)]
+pub struct Monkey {
+    pub name: String,
+    pub kind: MonkeyType
+}
+
+pub fn read_monkeys_from_stdin() -> Vec<Monkey> {
+    let mut v = vec![];
+    let mut line = String::new();
+    while std::io::stdin().read_line(&mut line).unwrap() > 0 {
+        let name = String::from(&line[0..4]);
+        let monkey = match line.chars().nth(6).unwrap() {
+            '0'..='9' => {
+                let n = line[6..line.len()-1].parse::<i64>().unwrap();
+                Monkey { name, kind: MonkeyType::Num(n) }
+            },
+            _ => {
+                let m1 = String::from(&line[6..10]);
+                let m2 = String::from(&line[13..17]);
+                let op = Operation { m1, m2, op: line.chars().nth(11).unwrap() };
+                Monkey { name, kind: MonkeyType::Op(op) }
+            }
+        };
+        v.push(monkey);
+        line.clear();
+    }
+    v
+}
+
+pub fn apply_op(n1: i64, n2: i64, op: &Operation) -> i64 {
+    match op.op {
+        '+' => n1 + n2,
+        '-' => n1 - n2,
+        '*' => n1 * n2,
+        '/' => n1 / n2,
+        _ => panic!("invalid operator")
+    }
+}