rs: add «1700. Number of Students Unable to Eat Lunch»

Signed-off-by: Matej Focko <mfocko@redhat.com>

rs/number-of-students-unable-to-eat-lunch.rs

@@ -0,0 +1,20 @@
+impl Solution {
+    pub fn count_students(students: Vec<i32>, sandwiches: Vec<i32>) -> i32 {
+        let mut students_by_sandwiches = vec![0; 2];
+        for student in &students {
+            students_by_sandwiches[*student as usize] += 1;
+        }
+
+        for sandwich in &sandwiches {
+            let idx = *sandwich as usize;
+
+            if students_by_sandwiches[idx] <= 0 {
+                return students_by_sandwiches[(idx + 1) % 2];
+            }
+
+            students_by_sandwiches[idx] -= 1;
+        }
+
+        0
+    }
+}