commit e1d47d6a28dd0b835f20ca63bfb969a7de955568feb8dd6e8caa6c32736fb34b
Author: professorwaltwood <professor@waltwood.dev>
Date:   Sun Aug 2 17:47:53 2026 +1000

    feat(dosages): added library function to calculate optimal combination of medicines for desired dosage

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..b676c71
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,8 @@
+/target
+
+
+# Added by cargo
+#
+# already existing elements were commented out
+
+#/target
diff --git a/Cargo.lock b/Cargo.lock
new file mode 100644
index 0000000..28fba96
--- /dev/null
+++ b/Cargo.lock
@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "lsdp"
+version = "0.1.0"
diff --git a/Cargo.toml b/Cargo.toml
new file mode 100644
index 0000000..dd6e720
--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,6 @@
+[package]
+name = "lsdp"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
diff --git a/src/combo_graph.rs b/src/combo_graph.rs
new file mode 100644
index 0000000..d57f39e
--- /dev/null
+++ b/src/combo_graph.rs
@@ -0,0 +1,137 @@
+use std::{cmp::max, collections::HashMap, ops::Index};
+
+pub struct ComboNode {
+    combo: Vec<u32>,
+    weight: u32,
+}
+
+impl Index<usize> for ComboNode {
+    type Output = u32;
+    fn index(&self, index: usize) -> &Self::Output {
+        self.combo.index(index)
+    }
+}
+
+impl ComboNode {
+    pub fn weight(&self) -> u32 {
+        self.weight
+    }
+
+    pub fn new(combo: Vec<u32>) -> Self {
+        let sum = combo.iter().sum();
+        Self { combo, weight: sum }
+    }
+
+    pub fn get_neighbours(&self) -> impl Iterator<Item = ComboNode> {
+        (0..self.combo.len()).map(|i| {
+            let mut combo = self.combo.clone();
+            combo[i] += 1;
+            Self {
+                combo,
+                weight: self.weight + 1,
+            }
+        })
+    }
+}
+
+pub struct ComboGraph {
+    nodes: HashMap<u32, ComboNode>,
+    values: Vec<u32>,
+    target: u32,
+    queue: Vec<ComboNode>,
+}
+
+impl ComboGraph {
+    pub fn new(mut values: Vec<u32>, target: u32) -> Self {
+        // ensure values is sorted
+        values.sort_unstable();
+        let num_values = values.len();
+        Self {
+            nodes: HashMap::new(),
+            values,
+            target,
+            queue: vec![ComboNode::new(vec![0; num_values])],
+        }
+    }
+
+    pub fn closest_node_target(&self) -> Option<&ComboNode> {
+        let closest = self
+            .nodes
+            .iter()
+            // Treat a zero difference as a difference of 1 to accomodate for rounding
+            .map(|(pos, combo)| (max(self.target.abs_diff(*pos), 1), combo.weight(), pos))
+            .min()?;
+
+        self.nodes.get(&closest.2)
+    }
+
+    /// Visit a combo and calculate its position and weight
+    pub fn visit(&mut self, node: ComboNode) -> bool {
+        let mut pos = 0;
+
+        for i in 0..self.values.len() {
+            pos += self.values[i] * node[i];
+        }
+
+        // Check if pos already found with less weight
+        let current = self.nodes.get(&pos);
+        if let Some(combo) = current {
+            if combo.weight() > node.weight() {
+                // should never happen
+                panic!("Found better path second");
+            }
+            return false;
+        } else if pos == self.target {
+            self.nodes.insert(pos, node);
+            return true;
+        } else if pos < self.target {
+            node.get_neighbours().for_each(|n| {
+                self.queue.push(n);
+            });
+        }
+        self.nodes.insert(pos, node);
+
+        false
+    }
+
+    /// grows the graph to find the optimal path
+    pub fn grow(&mut self) -> bool {
+        let mut next = self.queue.pop();
+        while let Some(node) = next {
+            if self.visit(node) {
+                return true;
+            }
+            next = self.queue.pop();
+        }
+        false
+    }
+
+    pub fn target_combo(&self) -> Option<Vec<u32>> {
+        let combo = self.nodes.get(&self.target)?;
+        Some(
+            (0..self.values.len())
+                .map(|i| vec![self.values[i]; combo[i] as usize])
+                .flatten()
+                .collect(),
+        )
+    }
+
+    pub fn closest_combo(&self) -> Option<Vec<u32>> {
+        let combo = self.closest_node_target()?;
+        Some(
+            (0..self.values.len())
+                .map(|i| vec![self.values[i]; combo[i] as usize])
+                .flatten()
+                .collect(),
+        )
+    }
+}
+
+pub fn find_optimal_combo(strengths: Vec<u32>, target: u32, rounded: bool) -> Vec<u32> {
+    let mut graph = ComboGraph::new(strengths, target);
+    if graph.grow() && !rounded {
+        graph.target_combo().expect("grow signalled target hit")
+    } else {
+        graph.closest_combo().expect("non empty graph")
+    }
+}
diff --git a/src/factor.rs b/src/factor.rs
new file mode 100644
index 0000000..3a8ca4c
--- /dev/null
+++ b/src/factor.rs
@@ -0,0 +1,101 @@
+/// calculate greatest common factor
+/// requires a > b
+fn gcf(mut a: u32, mut b: u32) -> u32 {
+    let mut rem = a % b;
+
+    while rem != 0 {
+        a = b;
+        b = rem;
+        rem = a % b;
+    }
+    b
+}
+
+/// Calculate gcf of vector
+fn gcfv(v: &Vec<u32>) -> u32 {
+    let mut i = 1;
+    let mut cgcf = v[0]; // start with first item
+    let mut a;
+    let mut b;
+    while i < v.len() {
+        if cgcf >= v[i] {
+            a = cgcf;
+            b = v[i];
+        } else {
+            a = v[i];
+            b = cgcf;
+        }
+        cgcf = gcf(a, b);
+
+        i += 1;
+    }
+
+    cgcf
+}
+
+pub fn factorise(strengths: &mut Vec<u32>) -> u32 {
+    let factor = gcfv(strengths);
+    if factor == 1 {
+        return factor;
+    }
+    for s in strengths.iter_mut() {
+        *s = *s / factor;
+    }
+    factor
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn gcf_base_case() {
+        assert_eq!(gcf(1, 1), 1);
+    }
+
+    #[test]
+    fn gcf_standard_case() {
+        assert_eq!(gcf(1071, 462), 21)
+    }
+
+    #[test]
+    fn gcf_coprime_case() {
+        assert_eq!(gcf(1071, 461), 1)
+    }
+
+    #[test]
+    fn gcfv_base_case() {
+        assert_eq!(gcfv(&vec![1]), 1);
+    }
+
+    #[test]
+    fn gcfv_standard_case() {
+        assert_eq!(gcfv(&vec![1071, 462, 42, 105]), 21)
+    }
+
+    #[test]
+    fn gcfv_coprime_case() {
+        assert_eq!(gcfv(&vec![1071, 105, 42, 461]), 1)
+    }
+
+    #[test]
+    fn factorise_base_case() {
+        let mut s = vec![1];
+        assert_eq!(factorise(&mut s), 1);
+        assert_eq!(s, vec![1]);
+    }
+
+    #[test]
+    fn factorise_standard_case() {
+        let mut s = vec![1071, 462, 42, 105];
+        assert_eq!(factorise(&mut s), 21);
+        assert_eq!(s, vec![51, 22, 2, 5]);
+    }
+
+    #[test]
+    fn factorise_coprime_case() {
+        let mut s = vec![1071, 105, 42, 461];
+        assert_eq!(factorise(&mut s), 1);
+        assert_eq!(s, vec![1071, 105, 42, 461]);
+    }
+}
diff --git a/src/lib.rs b/src/lib.rs
new file mode 100644
index 0000000..859c3fa
--- /dev/null
+++ b/src/lib.rs
@@ -0,0 +1,71 @@
+mod combo_graph;
+mod factor;
+
+use crate::combo_graph::find_optimal_combo;
+use crate::factor::factorise;
+
+/// Algorithm:
+/// 1. factorise strengths by GCF
+/// 2. Perform DFS search on strength combos starting from full largest strength
+/// 3. use efficiencies from dynamic programming to prune cases already calculated
+///
+/// ```
+/// use lsdp::calculate_combo;
+/// let combo = calculate_combo(173, vec![20, 57]);
+/// assert_eq!(combo, vec![20, 20, 20, 57, 57]);
+/// ```
+///
+pub fn calculate_combo(mut target: u32, mut strengths: Vec<u32>) -> Vec<u32> {
+    if strengths.len() == 0 {
+        return vec![];
+    }
+
+    let factor = factorise(&mut strengths);
+    let mut rounded = false;
+
+    if factor != 1 {
+        if target % factor != 0 {
+            let f_target: f64 = target as f64 / factor as f64;
+            target = f_target.round() as u32;
+            rounded = true;
+        } else {
+            target /= factor;
+            rounded = false;
+        }
+    }
+
+    let combo = find_optimal_combo(strengths, target, rounded);
+
+    combo.iter().map(|s| s * factor).collect()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn base_case() {
+        assert_eq!(calculate_combo(1, vec![1]), vec![1]);
+    }
+
+    #[test]
+    fn test_basic() {
+        assert_eq!(
+            calculate_combo(245, vec![50, 20, 5]),
+            vec![5, 20, 20, 50, 50, 50, 50]
+        );
+    }
+
+    #[test]
+    fn test_basic_close() {
+        assert_eq!(
+            calculate_combo(245, vec![50, 20, 4]),
+            vec![4, 20, 20, 50, 50, 50, 50]
+        );
+    }
+
+    #[test]
+    fn test_no_exact() {
+        assert_eq!(calculate_combo(173, vec![20, 57]), vec![20, 20, 20, 57, 57]);
+    }
+}