Fix clippy warnings (TheAlgorithms#113)

* Fix clippy idiomatic rust warnings

* Fix clippy lint in heap.rs

Allows MinHeap and MaxHeap new methods to return Heap

Fixes incorrect is_empty() implementation. is_empty should return true
when self.len() == 0.

* Fix clippy lint

This changes to use -= instead of manually implementing.
Removes a lifetime that can be elided.

* Turn on clippy warning failure in travis.yml

Author: boydjohnson

.travis.yml

@@ -5,5 +5,5 @@ before_script:
   - rustup component add clippy
 script:
   - cargo fmt --all -- --check
-  - cargo clippy
+  - cargo clippy --all -- -D warnings
   - cargo test

src/data_structures/b_tree.rs

@@ -68,10 +68,11 @@ impl BTreeProps {
             }
             None => Vec::with_capacity(self.max_keys),
         };
-        let mut right_children = None;
-        if !child.is_leaf() {
-            right_children = Some(child.children.split_off(self.mid_key_index + 1));
-        }
+        let right_children = if !child.is_leaf() {
+            Some(child.children.split_off(self.mid_key_index + 1))
+        } else {
+            None
+        };
         let new_child_node: Node<T> = Node::new(self.degree, Some(right_keys), right_children);
 
         parent.keys.insert(child_index, middle_key);

src/data_structures/heap.rs

@@ -34,7 +34,7 @@ where
     }
 
     pub fn is_empty(&self) -> bool {
-        self.len() > 0
+        self.len() == 0
     }
 
     pub fn add(&mut self, value: T) {
@@ -135,6 +135,7 @@ where
 pub struct MinHeap;
 
 impl MinHeap {
+    #[allow(clippy::new_ret_no_self)]
     pub fn new<T>() -> Heap<T>
     where
         T: Default + Ord,
@@ -146,6 +147,7 @@ impl MinHeap {
 pub struct MaxHeap;
 
 impl MaxHeap {
+    #[allow(clippy::new_ret_no_self)]
     pub fn new<T>() -> Heap<T>
     where
         T: Default + Ord,

src/data_structures/linked_list.rs

@@ -58,7 +58,7 @@ impl<T> LinkedList<T> {
         self.get_ith_node(self.start, index)
     }
 
-    fn get_ith_node<'a>(&'a mut self, node: Option<NonNull<Node<T>>>, index: i32) -> Option<&'a T> {
+    fn get_ith_node(&mut self, node: Option<NonNull<Node<T>>>, index: i32) -> Option<&T> {
         match node {
             None => None,
             Some(next_ptr) => match index {

src/dynamic_programming/longest_common_subsequence.rs

@@ -30,12 +30,12 @@ pub fn longest_common_subsequence(a: &str, b: &str) -> String {
     while i > 0 && j > 0 {
         if a[i - 1] == b[j - 1] {
             result.push(a[i - 1]);
-            i = i - 1;
-            j = j - 1;
+            i -= 1;
+            j -= 1;
         } else if solutions[i - 1][j] > solutions[i][j - 1] {
-            i = i - 1;
+            i -= 1;
         } else {
-            j = j - 1;
+            j -= 1;
         }
     }