make calculate recall fn clear

Signed-off-by: Keming <kemingy94@gmail.com>

src/utils.rs

@@ -351,15 +351,15 @@ where
 
 /// Calculate the recall.
 pub fn calculate_recall(truth: &[i32], res: &[i32], topk: usize) -> f32 {
+    assert_eq!(res.len(), topk);
     let mut count = 0;
-    let length = topk.min(truth.len());
-    for t in truth.iter().take(length) {
-        for y in res.iter().take(length.min(res.len())) {
-            if *t == *y {
+    for id in res {
+        for t in truth.iter().take(topk) {
+            if *id == *t {
                 count += 1;
                 break;
             }
         }
     }
-    (count as f32) / (length as f32)
+    (count as f32) / (topk as f32)
 }