From 80e891268a85d73b85690f4bf0ba81eee53726bb Mon Sep 17 00:00:00 2001
From: mehbark <terezi@pyrope.net>
Date: Wed, 4 Jan 2023 22:34:46 -0500
Subject: [PATCH] initial

---
 Cargo.lock    |  7 +++++
 Cargo.toml    |  8 +++++
 src/board.rs  | 84 +++++++++++++++++++++++++++++++++++++++++++++++++++
 src/main.rs   | 11 +++++++
 src/solver.rs | 63 ++++++++++++++++++++++++++++++++++++++
 5 files changed, 173 insertions(+)
 create mode 100644 Cargo.lock
 create mode 100644 Cargo.toml
 create mode 100644 src/board.rs
 create mode 100644 src/main.rs
 create mode 100644 src/solver.rs

diff --git a/Cargo.lock b/Cargo.lock
new file mode 100644
index 0000000..70c2396
--- /dev/null
+++ b/Cargo.lock
@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "most-chips-needed-for-bingo-board"
+version = "0.1.0"
diff --git a/Cargo.toml b/Cargo.toml
new file mode 100644
index 0000000..7063b0e
--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,8 @@
+[package]
+name = "most-chips-needed-for-bingo-board"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
diff --git a/src/board.rs b/src/board.rs
new file mode 100644
index 0000000..15aa398
--- /dev/null
+++ b/src/board.rs
@@ -0,0 +1,84 @@
+use std::array;
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub struct Board {
+    checked: [bool; 25],
+}
+
+// a u32 would be much more efficient (only need 25 bits)
+
+impl Board {
+    pub fn new() -> Self {
+        let checked = array::from_fn(|i| i == Self::idx(2, 2));
+
+        Self { checked }
+    }
+
+    pub fn new_without_center_dot() -> Self {
+        let checked = array::from_fn(|_| false);
+
+        Self { checked }
+    }
+
+    fn idx(x: usize, y: usize) -> usize {
+        x + y * 5
+    }
+
+    fn checked_at(&self, x: usize, y: usize) -> bool {
+        self.checked[Self::idx(x, y)]
+    }
+
+    fn checked_at_idx(&self, idx: usize) -> bool {
+        self.checked[idx]
+    }
+
+    pub fn num_chips(&self) -> usize {
+        self.checked.iter().filter(|b| **b).count()
+    }
+
+    pub fn is_done(&self) -> bool {
+        self.rows()
+            .chain(self.cols())
+            .chain(self.diags())
+            .any(and_all)
+    }
+
+    fn rows(&self) -> impl Iterator<Item = [bool; 5]> + '_ {
+        (0..5).map(|y| array::from_fn(|x| self.checked_at(x, y)))
+    }
+
+    fn cols(&self) -> impl Iterator<Item = [bool; 5]> + '_ {
+        (0..5).map(|x| array::from_fn(|y| self.checked_at(x, y)))
+    }
+
+    fn diags(&self) -> impl Iterator<Item = [bool; 5]> + '_ {
+        [
+            array::from_fn(|i| self.checked_at(i, i)),
+            array::from_fn(|i| self.checked_at(i, 4 - i)),
+        ]
+        .into_iter()
+    }
+
+    fn with_checked(&self, at: usize) -> Self {
+        let mut new = *self;
+        new.checked[at] = true;
+        new
+    }
+
+    pub fn successors(&self) -> impl Iterator<Item = Self> + '_ {
+        self.checked
+            .into_iter()
+            .enumerate()
+            .filter_map(|(i, checked)| {
+                if checked {
+                    None
+                } else {
+                    Some(self.with_checked(i))
+                }
+            })
+    }
+}
+
+fn and_all<const N: usize>(bs: [bool; N]) -> bool {
+    bs.iter().all(|b| *b)
+}
diff --git a/src/main.rs b/src/main.rs
new file mode 100644
index 0000000..354cf16
--- /dev/null
+++ b/src/main.rs
@@ -0,0 +1,11 @@
+mod board;
+mod solver;
+
+use crate::solver::solution;
+
+fn main() {
+    let solution = solution();
+    eprintln!("The maximum number of chips needed for a 5x5 bingo board that starts with the center filled is:");
+    println!("{solution}");
+    eprintln!("(This assumes that people want to fill their winning square, which does make sense for showing that you won I suppose)");
+}
diff --git a/src/solver.rs b/src/solver.rs
new file mode 100644
index 0000000..533aed8
--- /dev/null
+++ b/src/solver.rs
@@ -0,0 +1,63 @@
+use crate::board::Board;
+use std::collections::HashSet;
+
+pub fn solution() -> usize {
+    let mut solver = Solver::new();
+    solver.step_until_pointless();
+    solver.most_checked()
+}
+
+// there is definitely reflectional/rotational symmetry that could be utilized
+
+#[derive(Debug, Clone)]
+struct Solver {
+    end_states: HashSet<Board>,
+    in_progress_states: HashSet<Board>,
+    handled_states: HashSet<Board>,
+}
+
+impl Solver {
+    fn new() -> Self {
+        Self {
+            end_states: HashSet::new(),
+            in_progress_states: HashSet::from([Board::new()]),
+            handled_states: HashSet::new(),
+        }
+    }
+
+    fn most_checked(&self) -> usize {
+        self.end_states.iter().map(Board::num_chips).max().unwrap()
+    }
+
+    fn step_until_pointless(&mut self) {
+        loop {
+            let prev_end_state_count = self.end_states.len();
+            dbg!(prev_end_state_count);
+
+            self.step();
+
+            if !self.end_states.is_empty() && self.end_states.len() == prev_end_state_count {
+                break;
+            }
+        }
+    }
+
+    fn step(&mut self) {
+        let mut new_end_states = HashSet::new();
+        let mut new_ip_states = HashSet::new();
+
+        for state in &self.in_progress_states {
+            for succ in state.successors() {
+                if succ.is_done() {
+                    new_end_states.insert(succ);
+                } else if !self.handled_states.contains(&succ) {
+                    new_ip_states.insert(succ);
+                }
+            }
+        }
+
+        self.end_states.extend(new_end_states);
+        self.handled_states.extend(self.in_progress_states.iter());
+        self.in_progress_states = new_ip_states;
+    }
+}