feat: add rust solution to lc problem: No.2316 (doocs#1859)

No.2316.Count Unreachable Pairs of Nodes in an Undirected Graph

Author: ifmagic

solution/2300-2399/2316.Count Unreachable Pairs of Nodes in an Undirected Graph/README.md

@@ -226,6 +226,45 @@ function countPairs(n: number, edges: number[][]): number {
 }
 ```
 
+### **Rust**
+
+```rust
+impl Solution {
+    pub fn count_pairs(n: i32, edges: Vec<Vec<i32>>) -> i64 {
+        let n = n as usize;
+        let mut g = vec![vec![]; n];
+        let mut vis = vec![false; n];
+        for e in edges {
+            let u = e[0] as usize;
+            let v = e[1] as usize;
+            g[u].push(v);
+            g[v].push(u);
+        }
+
+        fn dfs(g: &Vec<Vec<usize>>, vis: &mut Vec<bool>, u: usize) -> i64 {
+            if vis[u] {
+                return 0;
+            }
+            vis[u] = true;
+            let mut cnt = 1;
+            for &v in &g[u] {
+                cnt += dfs(g, vis, v);
+            }
+            cnt
+        }
+
+        let mut ans = 0;
+        let mut s = 0;
+        for u in 0..n {
+            let t = dfs(&g, &mut vis, u);
+            ans += t * s;
+            s += t;
+        }
+        ans
+    }
+}
+```
+
 ### **...**
 
 ```

solution/2300-2399/2316.Count Unreachable Pairs of Nodes in an Undirected Graph/README_EN.md

@@ -214,6 +214,45 @@ function countPairs(n: number, edges: number[][]): number {
 }
 ```
 
+### **Rust**
+
+```rust
+impl Solution {
+    pub fn count_pairs(n: i32, edges: Vec<Vec<i32>>) -> i64 {
+        let n = n as usize;
+        let mut g = vec![vec![]; n];
+        let mut vis = vec![false; n];
+        for e in edges {
+            let u = e[0] as usize;
+            let v = e[1] as usize;
+            g[u].push(v);
+            g[v].push(u);
+        }
+
+        fn dfs(g: &Vec<Vec<usize>>, vis: &mut Vec<bool>, u: usize) -> i64 {
+            if vis[u] {
+                return 0;
+            }
+            vis[u] = true;
+            let mut cnt = 1;
+            for &v in &g[u] {
+                cnt += dfs(g, vis, v);
+            }
+            cnt
+        }
+
+        let mut ans = 0;
+        let mut s = 0;
+        for u in 0..n {
+            let t = dfs(&g, &mut vis, u);
+            ans += t * s;
+            s += t;
+        }
+        ans
+    }
+}
+```
+
 ### **...**
 
 ```

solution/2300-2399/2316.Count Unreachable Pairs of Nodes in an Undirected Graph/Solution.rs

@@ -0,0 +1,34 @@
+impl Solution {
+    pub fn count_pairs(n: i32, edges: Vec<Vec<i32>>) -> i64 {
+        let n = n as usize;
+        let mut g = vec![vec![]; n];
+        let mut vis = vec![false; n];
+        for e in edges {
+            let u = e[0] as usize;
+            let v = e[1] as usize;
+            g[u].push(v);
+            g[v].push(u);
+        }
+
+        fn dfs(g: &Vec<Vec<usize>>, vis: &mut Vec<bool>, u: usize) -> i64 {
+            if vis[u] {
+                return 0;
+            }
+            vis[u] = true;
+            let mut cnt = 1;
+            for &v in &g[u] {
+                cnt += dfs(g, vis, v);
+            }
+            cnt
+        }
+
+        let mut ans = 0;
+        let mut s = 0;
+        for u in 0..n {
+            let t = dfs(&g, &mut vis, u);
+            ans += t * s;
+            s += t;
+        }
+        ans
+    }
+}