feat: add solution for last stone weight

Author: bujosa

src/easy/last_stone_weight.rs

@@ -0,0 +1,37 @@
+#![allow(dead_code)]
+use std::collections::BinaryHeap;
+
+fn last_stone_weight(stones: Vec<i32>) -> i32 {
+    let mut max_heap = BinaryHeap::from(stones);
+    while max_heap.len() > 1 {
+        let stone1 = max_heap.pop().unwrap();
+        let stone2 = max_heap.pop().unwrap();
+        if stone1 != stone2 {
+            max_heap.push(stone1 - stone2);
+        }
+    }
+    *max_heap.peek().unwrap_or(&0)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_1() {
+        let stones = vec![2, 7, 4, 1, 8, 1];
+        assert_eq!(last_stone_weight(stones), 1);
+    }
+
+    #[test]
+    fn test_2() {
+        let stones = vec![1, 3];
+        assert_eq!(last_stone_weight(stones), 2);
+    }
+
+    #[test]
+    fn test_3() {
+        let stones = vec![1];
+        assert_eq!(last_stone_weight(stones), 1);
+    }
+}