Sub-optimal recursive solution

.gitignore

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+/target

Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+[[package]]
+name = "kv"
+version = "0.0.1"

Cargo.toml

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+[package]
+name = "kv"
+version = "0.0.1"
+authors = ["Arne Keller <arne.keller@posteo.de>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

src/lib.rs

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+pub type Variable = usize;
+
+pub const A: Variable = 1 << 0;
+pub const B: Variable = 1 << 1;
+pub const C: Variable = 1 << 2;
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum Output {
+	Zero,
+	One,
+	Any
+}
+
+use Output::*;
+
+impl Output {
+	fn to_num(self) -> usize {
+		match self {
+		    Zero => 0,
+		    One => 1,
+		    Any => todo!()
+		}
+	}
+
+	fn invert(self) -> Self {
+		match self {
+		    Zero => One,
+		    One => Zero,
+		    Any => Any
+		}
+	}
+}
+
+impl From<usize> for Output {
+    fn from(x: usize) -> Self {
+        match x {
+			0 => Zero,
+			1 => One,
+			_ => todo!()
+		}
+    }
+}
+
+pub type FunctionSpec = Vec<Output>;
+
+pub fn find_groups(func: &FunctionSpec, vars: &mut [Variable], typ: Output) -> Vec<Vec<(Variable, Output)>> {
+	find_recursive(func, vars, typ, vec![], 0, !0)
+}
+
+fn find_recursive(func: &FunctionSpec, vars: &mut [Variable], typ: Output, set: Vec<(Variable, Output)>, mask: Variable, inv_mask: Variable) -> Vec<Vec<(Variable, Output)>> {
+	let mut groups = Vec::new();
+	for i in 0..vars.len() {
+		let var = vars[i];
+		if var == 0 {
+			continue; // already set
+		}
+		let mut fits_var_1 = true;
+		let mut fits_var_0 = true;
+		for input in 0..func.len() {
+			if !(input & inv_mask == input && input | mask == input) {
+				continue;
+			}
+			if input & var != 0 {
+				if func[input] == typ.invert() {
+					fits_var_1 = false;
+				}
+			} else {
+				if func[input] == typ.invert() {
+					fits_var_0 = false;
+				}
+			}
+			if !fits_var_0 && !fits_var_1 {
+				break;
+			}
+		}
+		if fits_var_1 {
+			let mut new_group = set.clone();
+			new_group.push((var, One));
+			groups.push(new_group);
+		} else {
+			let mut set2 = set.clone();
+			set2.push((var, One));
+			vars[i] = 0;
+			groups.extend(find_recursive(func, vars, typ, set2, mask | var, inv_mask));
+			vars[i] = var;
+		}
+
+		if fits_var_0 {
+			let mut new_group = set.clone();
+			new_group.push((var, Zero));
+			groups.push(new_group);
+		} else {
+			let mut set2 = set.clone();
+			set2.push((var, Zero));
+			vars[i] = 0;
+			groups.extend(find_recursive(func, vars, typ, set2, mask, inv_mask ^ var));
+			vars[i] = var;
+		}
+	}
+	groups
+}

src/main.rs

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+use kv::*;
+use kv::Output::*;
+
+fn main() {
+	let function = vec![0, 0, 1, 0, 0, 1, 1, 1].into_iter().map(Into::into).collect();
+	let groups = find_groups(&function, &mut [A, B, C], Zero);
+	for x in groups {
+		println!("{:?}", x);
+	}
+}