polish rust (#1790)

* polish graph

* Update graph

Author: rongyi

codes/rust/chapter_graph/graph_adjacency_list.rs

@@ -11,7 +11,7 @@ use std::collections::HashMap;
 /* 基于邻接表实现的无向图类型 */
 pub struct GraphAdjList {
     // 邻接表，key：顶点，value：该顶点的所有邻接顶点
-    pub adj_list: HashMap<Vertex, Vec<Vertex>>,
+    pub adj_list: HashMap<Vertex, Vec<Vertex>>, // maybe HashSet<Vertex> for value part is better?
 }
 
 impl GraphAdjList {
@@ -38,31 +38,27 @@ impl GraphAdjList {
 
     /* 添加边 */
     pub fn add_edge(&mut self, vet1: Vertex, vet2: Vertex) {
-        if !self.adj_list.contains_key(&vet1) || !self.adj_list.contains_key(&vet2) || vet1 == vet2
-        {
+        if vet1 == vet2 {
             panic!("value error");
         }
         // 添加边 vet1 - vet2
-        self.adj_list.get_mut(&vet1).unwrap().push(vet2);
-        self.adj_list.get_mut(&vet2).unwrap().push(vet1);
+        self.adj_list.entry(vet1).or_default().push(vet2);
+        self.adj_list.entry(vet2).or_default().push(vet1);
     }
 
     /* 删除边 */
     #[allow(unused)]
     pub fn remove_edge(&mut self, vet1: Vertex, vet2: Vertex) {
-        if !self.adj_list.contains_key(&vet1) || !self.adj_list.contains_key(&vet2) || vet1 == vet2
-        {
+        if vet1 == vet2 {
             panic!("value error");
         }
         // 删除边 vet1 - vet2
         self.adj_list
-            .get_mut(&vet1)
-            .unwrap()
-            .retain(|&vet| vet != vet2);
+            .entry(vet1)
+            .and_modify(|v| v.retain(|&e| e != vet2));
         self.adj_list
-            .get_mut(&vet2)
-            .unwrap()
-            .retain(|&vet| vet != vet1);
+            .entry(vet2)
+            .and_modify(|v| v.retain(|&e| e != vet1));
     }
 
     /* 添加顶点 */
@@ -77,9 +73,6 @@ impl GraphAdjList {
     /* 删除顶点 */
     #[allow(unused)]
     pub fn remove_vertex(&mut self, vet: Vertex) {
-        if !self.adj_list.contains_key(&vet) {
-            panic!("value error");
-        }
         // 在邻接表中删除顶点 vet 对应的链表
         self.adj_list.remove(&vet);
         // 遍历其他顶点的链表，删除所有包含 vet 的边

codes/rust/chapter_graph/graph_adjacency_matrix.rs

@@ -45,7 +45,7 @@ impl GraphAdjMat {
         // 在邻接矩阵中添加一行
         self.adj_mat.push(vec![0; n]);
         // 在邻接矩阵中添加一列
-        for row in &mut self.adj_mat {
+        for row in self.adj_mat.iter_mut() {
             row.push(0);
         }
     }
@@ -60,7 +60,7 @@ impl GraphAdjMat {
         // 在邻接矩阵中删除索引 index 的行
         self.adj_mat.remove(index);
         // 在邻接矩阵中删除索引 index 的列
-        for row in &mut self.adj_mat {
+        for row in self.adj_mat.iter_mut() {
             row.remove(index);
         }
     }

codes/rust/chapter_graph/graph_bfs.rs

@@ -22,8 +22,7 @@ fn graph_bfs(graph: GraphAdjList, start_vet: Vertex) -> Vec<Vertex> {
     let mut que = VecDeque::new();
     que.push_back(start_vet);
     // 以顶点 vet 为起点，循环直至访问完所有顶点
-    while !que.is_empty() {
-        let vet = que.pop_front().unwrap(); // 队首顶点出队
+    while let Some(vet) = que.pop_front() {
         res.push(vet); // 记录访问顶点
 
         // 遍历该顶点的所有邻接顶点