added hashmap branch

sparse_vector/src/main.rs

@@ -1,3 +1,4 @@
+use std::collections::HashMap;
 use std::ops::{Add, Mul, Sub};
 use std::thread;
 use std::time::Instant;
@@ -12,8 +13,7 @@ static ALLOC: jemallocator::Jemalloc = jemallocator::Jemalloc;
 
 /// Only stores more efficiently when at least 50% of all elements are zeros
 pub struct SparseVec {
-    values: Vec<f64>,
-    indices: Vec<usize>,
+    data: HashMap<usize, f64>
 }
 
 impl SparseVec {
@@ -21,9 +21,8 @@ impl SparseVec {
     pub fn dot(&self, other: &SparseVec) -> f64 {
         let mut sum = 0.0;
 
-        for index in 0..other.indices.len() {
-            // exponential search for an element in the second vector to have the same index
-            sum += binary_search(self.indices[index], &other.indices, &other.values) * self.values[index];
+        for (k, v) in self.data.iter() {
+            sum += v * other.data.get(k).unwrap_or(&0.0);
         }
 
         sum
@@ -32,49 +31,21 @@ impl SparseVec {
     pub fn new(elements: usize, non_null: f64) -> Self {
         let non_zero_elements = (elements as f64 * non_null) as usize;
 
-        let mut values = Vec::with_capacity(non_zero_elements);
-        let mut indices = Vec::with_capacity(non_zero_elements);
+        let mut data = HashMap::with_capacity(non_zero_elements);
 
         let mut rng = rand::thread_rng();
 
         for i in 0..non_zero_elements {
-            values.push(0.5);
-
             let idx = i as f32 / non_zero_elements as f32 * (elements as f32 - 4.0) + rng.gen_range(0.0..3.0);
-            indices.push(idx as usize);
+            data.insert(idx as usize, 0.5);
         }
 
         Self {
-            values,
-            indices
+            data
         }
     }
 }
 
-#[inline]
-fn binary_search(target: usize, indices: &[usize], values: &[f64]) -> f64 {
-    let mut range = 0..indices.len();
-    loop {
-        let mut median = (range.end - range.start) >> 1;
-        if median == 0 {
-            break;
-        }
-        median += range.start;
-
-        if indices[median] == target {
-            return values[median];
-        }
-
-        if indices[median] > target {
-            range.end = median;
-        } else {
-            range.start = median;
-        }
-    }
-
-    0.0
-}
-
 macro_rules! time {
     ($name:literal, $block:expr) => {{
         let start = Instant::now();