Implement Huffman encoding

src/huffman.rs

@@ -1,5 +1,69 @@
+use std::cmp::max;
+use std::cmp::min;
 
+#[derive(Debug)]
 pub struct HuffmanAlphabet {
-	pub length: u32,
-	pub frequencies: Vec<u32>,
+    pub length: usize,
+    pub frequencies: Vec<u64>,
+}
+
+#[derive(Debug)]
+struct HuffmanTreeNode {
+    frequency: u64,
+    left: Option<Box<HuffmanTreeNode>>,
+    right: Option<Box<HuffmanTreeNode>>,
+}
+
+fn max_depth(tree: &HuffmanTreeNode) -> usize {
+    let mut depth_left = 0;
+    if let Some(node_left) = &tree.left {
+        depth_left = 1 + max_depth(&node_left);
+    }
+
+    let mut depth_right = 0;
+    if let Some(node_right) = &tree.right {
+        depth_right = 1 + max_depth(&node_right);
+    }
+
+    max(depth_left, depth_right)
+}
+
+fn min_depth(tree: &HuffmanTreeNode) -> usize {
+    let mut depth_left = 0;
+    if let Some(node_left) = &tree.left {
+        depth_left = 1 + min_depth(&node_left);
+    }
+
+    let mut depth_right = 0;
+    if let Some(node_right) = &tree.right {
+        depth_right = 1 + min_depth(&node_right);
+    }
+
+    min(depth_left, depth_right)
+}
+
+pub fn build_huffman_tree(h: &HuffmanAlphabet) -> (usize, usize) {
+    let mut nodes: Vec<HuffmanTreeNode> = Vec::new();
+    for f in &h.frequencies {
+        let n = HuffmanTreeNode {
+            frequency: *f,
+            left: None,
+            right: None,
+        };
+        nodes.push(n);
+    }
+    nodes.sort_by(|a, b| b.frequency.cmp(&a.frequency));
+    while nodes.len() > 1 {
+        let a = nodes.pop().unwrap();
+        let b = nodes.pop().unwrap();
+        let n = HuffmanTreeNode {
+            frequency: a.frequency + b.frequency,
+            left: Some(Box::new(a)),
+            right: Some(Box::new(b)),
+        };
+        nodes.push(n);
+        nodes.sort_by(|a, b| b.frequency.cmp(&a.frequency));
+    }
+    let tree = nodes.pop().unwrap();
+    (min_depth(&tree), max_depth(&tree))
 }

src/k_clustering_big.rs

@@ -19,7 +19,6 @@ fn neighbors(a: u32, n: usize) -> Vec<u32> {
     r
 }
 
-
 pub fn k_clustering_big(g: &ImpliciteGraph) -> usize {
     let mut node_id_to_cluster_id: Vec<usize> = (0..g.len()).collect();
     let mut clusters: Vec<Vec<usize>> = (0..g.len()).map(|x| vec![x]).collect();

src/main.rs

@@ -1,5 +1,6 @@
 mod dijkstra;
 mod heap;
+mod huffman;
 mod jobs;
 mod k_clustering;
 mod k_clustering_big;
@@ -117,7 +118,9 @@ fn c3a2() {
 
 #[allow(dead_code)]
 fn c3a3() {
-	println!("continue here");
+    let h = util::read_huffman_alphabet("data/c3a3_huffman.txt").unwrap();
+    let r = huffman::build_huffman_tree(&h);
+    println!("r1 = {} r2 = {}", r.1, r.0);
 }
 
 fn main() {

src/util.rs

@@ -1,3 +1,4 @@
+use crate::huffman;
 use crate::jobs;
 use crate::k_clustering;
 use crate::k_clustering_big;
@@ -239,3 +240,23 @@ pub fn read_k_cluster_big(path: &str) -> Result<k_clustering_big::ImpliciteGraph
 
     Ok(g)
 }
+
+pub fn read_huffman_alphabet(path: &str) -> Result<huffman::HuffmanAlphabet, io::Error> {
+    let file = File::open(path)?;
+    let mut lines = BufReader::new(file).lines();
+    let line = lines.next().unwrap().unwrap();
+    let length = line.parse().unwrap();
+
+    let mut h = huffman::HuffmanAlphabet {
+        length: length,
+        frequencies: Vec::new(),
+    };
+
+    for line in lines {
+        let line = line?;
+        let frequency = line.parse().unwrap();
+        h.frequencies.push(frequency);
+    }
+    assert!(length == h.frequencies.len());
+    Ok(h)
+}