From 2fc0445901f59fc9f07531c30ebf88395f7cbba8 Mon Sep 17 00:00:00 2001
From: Arne Keller <arne.keller@posteo.de>
Date: Sat, 13 Mar 2021 11:43:24 +0100
Subject: [PATCH] Better combinatoric implementation

---
 Cargo.lock | 18 ++++++++++++
 Cargo.toml |  1 +
 src/lib.rs | 84 +++++++++++++++++++++++-------------------------------
 3 files changed, 54 insertions(+), 49 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index da6aa0e..08bc4ea 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1,5 +1,23 @@
 # This file is automatically @generated by Cargo.
 # It is not intended for manual editing.
+[[package]]
+name = "either"
+version = "1.6.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e78d4f1cc4ae33bbfc157ed5d5a5ef3bc29227303d595861deb238fcec4e9457"
+
+[[package]]
+name = "itertools"
+version = "0.10.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "37d572918e350e82412fe766d24b15e6682fb2ed2bbe018280caa810397cb319"
+dependencies = [
+ "either",
+]
+
 [[package]]
 name = "kv"
 version = "0.0.1"
+dependencies = [
+ "itertools",
+]
diff --git a/Cargo.toml b/Cargo.toml
index 581c07e..29e311c 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -7,3 +7,4 @@ edition = "2018"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+itertools = "0.10.0"
diff --git a/src/lib.rs b/src/lib.rs
index a490061..f857a88 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,3 +1,5 @@
+use itertools::Itertools;
+
 pub type Variable = usize;
 
 pub const A: Variable = 1 << 0;
@@ -43,59 +45,43 @@ impl From<usize> for Output {
 
 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;
+pub fn find_groups(func: &FunctionSpec, vars: &[Variable], typ: Output) -> Vec<Vec<(Variable, Output)>> {
+	let mut groups: Vec<Vec<(Variable, Output)>> = Vec::new();
+	for k in 1..vars.len()+1 {
+		for vars in vars.iter().combinations(k) {
+			for var_bits in 0..(1 << k) {
+				let var_setting: Vec<_> = vars
+						.iter()
+						.enumerate()
+						.map(|(i, &&var)| (var, ((var_bits >> i) & 1).into()))
+						.collect();
+				if groups.iter().any(|x| subset_of(x, &var_setting)) {
+					continue;
 				}
-			} else {
-				if func[input] == typ.invert() {
-					fits_var_0 = false;
+				let mut mask = 0;
+				let mut inv_mask = !0;
+				for (i, &&var) in vars.iter().enumerate() {
+					mask |= if ((var_bits >> i) & 1) == 1 { var } else { 0 };
+					inv_mask ^= if ((var_bits >> i) & 1) == 1 { 0 } else { var };
+				}
+				let mut fits = true;
+				for input in 0..func.len() {
+					if input | mask == input && input & inv_mask == input {
+						if func[input] == typ.invert() {
+							fits = false;
+							break;
+						}
+					}
+				}
+				if fits {
+					groups.push(var_setting);
 				}
 			}
-			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
+}
+
+fn subset_of<T: Eq>(a: &[T], b: &[T]) -> bool {
+	a.iter().all(|x| b.contains(x))
 }
\ No newline at end of file