Add len and is_empty to fenwicktree, segtree, and lazysegtree

src/fenwicktree.rs

@@ -53,6 +53,14 @@ impl<T: Clone + std::ops::AddAssign<T>> FenwickTree<T> {
         };
         self.accum(r) - self.accum(l)
     }
+    /// Returns the number of elements.
+    pub fn len(&self) -> usize {
+        self.n
+    }
+    /// Returns if the container is empty.
+    pub fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
 }
 
 #[cfg(test)]
@@ -67,6 +75,10 @@ mod tests {
         for i in 0..5 {
             bit.add(i, i as i64 + 1);
         }
+
+        assert_eq!(bit.len(), 5);
+        assert!(!bit.is_empty());
+
         assert_eq!(bit.sum(0..5), 15);
         assert_eq!(bit.sum(0..4), 10);
         assert_eq!(bit.sum(1..3), 5);

src/lazysegtree.rs

@@ -289,6 +289,15 @@ impl<F: MapMonoid> LazySegtree<F> {
         } {}
         0
     }
+
+    /// Returns the number of elements.
+    pub fn len(&self) -> usize {
+        self.n
+    }
+    /// Returns if the container is empty.
+    pub fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
 }
 
 pub struct LazySegtree<F>
@@ -381,6 +390,9 @@ mod tests {
         let mut segtree: LazySegtree<MaxAdd> = base.clone().into();
         check_segtree(&base, &mut segtree);
 
+        assert_eq!(segtree.len(), n);
+        assert!(!segtree.is_empty());
+
         let mut segtree = LazySegtree::<MaxAdd>::new(n);
         let mut internal = vec![i32::min_value(); n];
         for i in 0..n {

src/segtree.rs

@@ -233,6 +233,15 @@ impl<M: Monoid> Segtree<M> {
     fn update(&mut self, k: usize) {
         self.d[k] = M::binary_operation(&self.d[2 * k], &self.d[2 * k + 1]);
     }
+
+    /// Returns the number of elements.
+    pub fn len(&self) -> usize {
+        self.n
+    }
+    /// Returns if the container is empty.
+    pub fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
 }
 
 // Maybe we can use this someday
@@ -269,6 +278,9 @@ mod tests {
         let segtree: Segtree<Max<_>> = base.clone().into();
         check_segtree(&base, &segtree);
 
+        assert_eq!(segtree.len(), n);
+        assert!(!segtree.is_empty());
+
         let mut segtree = Segtree::<Max<_>>::new(n);
         let mut internal = vec![i32::min_value(); n];
         for i in 0..n {