rs: add «948. Bag of Tokens»

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

rs/bag-of-tokens.rs

@@ -0,0 +1,56 @@
+struct Solution {}
+impl Solution {
+    pub fn bag_of_tokens_score(mut tokens: Vec<i32>, mut power: i32) -> i32 {
+        if tokens.is_empty() {
+            return 0;
+        }
+
+        tokens.sort_unstable();
+
+        let mut i = 0;
+        let mut j = tokens.len() - 1;
+
+        let mut score = 0;
+        while i <= j {
+            if power >= tokens[i] {
+                // can trade score for power
+                power -= tokens[i];
+                score += 1;
+                i += 1;
+            } else if i < j && score > 0 {
+                // can trade power for score
+                score -= 1;
+                power += tokens[j];
+                j -= 1;
+            } else {
+                // no further action is possible
+                break;
+            }
+        }
+
+        score
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn example_1() {
+        assert_eq!(Solution::bag_of_tokens_score(vec![100], 50), 0);
+    }
+
+    #[test]
+    fn example_2() {
+        assert_eq!(Solution::bag_of_tokens_score(vec![200, 100], 150), 1);
+    }
+
+    #[test]
+    fn example_3() {
+        assert_eq!(
+            Solution::bag_of_tokens_score(vec![100, 200, 300, 400], 200),
+            2
+        );
+    }
+}