Added from scratch binary search implementation.

src/leetcode/binary_search.rs

@@ -1,8 +1,23 @@
+// pub fn search(numbers: Vec<i32>, target: i32) -> i32 {
+//     match numbers.binary_search(&target) {
+//         Ok(i) => i as i32,
+//         Err(_) => -1,
+//     }
+// }
+
+use std::cmp::Ordering;
+
 pub fn search(numbers: Vec<i32>, target: i32) -> i32 {
-    match numbers.binary_search(&target) {
-        Ok(i) => i as i32,
-        Err(_) => -1,
+    let (mut left, mut right) = (0, numbers.len());
+    while left < right {
+        let mid = left + (right - left) / 2;
+        match numbers[mid].cmp(&target) {
+            Ordering::Equal => return mid as i32,
+            Ordering::Less => left = mid + 1,
+            Ordering::Greater => right = mid,
+        }
     }
+    -1
 }
 
 #[cfg(test)]
@@ -11,11 +26,14 @@ mod tests {
 
     #[test]
     fn finds_element_index_when_it_exists() {
-        assert_eq!(4, search(vec![-1, 0, 3, 5, 9, 12], 9))
+        assert_eq!(4, search(vec![-1, 0, 3, 5, 9, 12], 9));
+        assert_eq!(0, search(vec![5], 5));
     }
 
     #[test]
     fn negative_one_when_element_does_not_exist() {
-        assert_eq!(-1, search(vec![-1, 0, 3, 5, 9, 12], 20))
+        assert_eq!(-1, search(vec![-1, 0, 3, 5, 9, 12], 20));
+        assert_eq!(-1, search(vec![-1, 0, 3, 5, 9, 12], 2));
+        assert_eq!(-1, search(vec![5], -5))
     }
 }