feat: add rust solution to lc problem: No.0216 (#1374)

Author: xzhseh

solution/0200-0299/0216.Combination Sum III/README.md

@@ -326,6 +326,39 @@ public:
 };
 ```
 
+### **Rust**
+
+```rust
+impl Solution {
+    #[allow(dead_code)]
+    pub fn combination_sum3(k: i32, n: i32) -> Vec<Vec<i32>> {
+        let mut ret = Vec::new();
+        let mut candidates = (1..=9).collect();
+        let mut cur_vec = Vec::new();
+        Self::dfs(n, k, 0, 0, &mut cur_vec, &mut candidates, &mut ret);
+        ret
+    }
+
+    #[allow(dead_code)]
+    fn dfs(target: i32, length: i32, cur_index: usize, cur_sum: i32, cur_vec: &mut Vec<i32>, candidates: &Vec<i32>, ans: &mut Vec<Vec<i32>>) {
+        if cur_sum > target || cur_vec.len() > length as usize {
+            // No answer for this
+            return;
+        }
+        if cur_sum == target && cur_vec.len() == length as usize {
+            // We get an answer
+            ans.push(cur_vec.clone());
+            return;
+        }
+        for i in cur_index..candidates.len() {
+            cur_vec.push(candidates[i]);
+            Self::dfs(target, length, i + 1, cur_sum + candidates[i], cur_vec, candidates, ans);
+            cur_vec.pop().unwrap();
+        }
+    }
+}
+```
+
 ### **Go**
 
 ```go

solution/0200-0299/0216.Combination Sum III/README_EN.md

@@ -283,6 +283,39 @@ public:
 };
 ```
 
+### **Rust**
+
+```rust
+impl Solution {
+    #[allow(dead_code)]
+    pub fn combination_sum3(k: i32, n: i32) -> Vec<Vec<i32>> {
+        let mut ret = Vec::new();
+        let mut candidates = (1..=9).collect();
+        let mut cur_vec = Vec::new();
+        Self::dfs(n, k, 0, 0, &mut cur_vec, &mut candidates, &mut ret);
+        ret
+    }
+
+    #[allow(dead_code)]
+    fn dfs(target: i32, length: i32, cur_index: usize, cur_sum: i32, cur_vec: &mut Vec<i32>, candidates: &Vec<i32>, ans: &mut Vec<Vec<i32>>) {
+        if cur_sum > target || cur_vec.len() > length as usize {
+            // No answer for this
+            return;
+        }
+        if cur_sum == target && cur_vec.len() == length as usize {
+            // We get an answer
+            ans.push(cur_vec.clone());
+            return;
+        }
+        for i in cur_index..candidates.len() {
+            cur_vec.push(candidates[i]);
+            Self::dfs(target, length, i + 1, cur_sum + candidates[i], cur_vec, candidates, ans);
+            cur_vec.pop().unwrap();
+        }
+    }
+}
+```
+
 ### **Go**
 
 ```go

solution/0200-0299/0216.Combination Sum III/Solution.rs

@@ -0,0 +1,28 @@
+impl Solution {
+    #[allow(dead_code)]
+    pub fn combination_sum3(k: i32, n: i32) -> Vec<Vec<i32>> {
+        let mut ret = Vec::new();
+        let mut candidates = (1..=9).collect();
+        let mut cur_vec = Vec::new();
+        Self::dfs(n, k, 0, 0, &mut cur_vec, &mut candidates, &mut ret);
+        ret
+    }
+
+    #[allow(dead_code)]
+    fn dfs(target: i32, length: i32, cur_index: usize, cur_sum: i32, cur_vec: &mut Vec<i32>, candidates: &Vec<i32>, ans: &mut Vec<Vec<i32>>) {
+        if cur_sum > target || cur_vec.len() > length as usize {
+            // No answer for this
+            return;
+        }
+        if cur_sum == target && cur_vec.len() == length as usize {
+            // We get an answer
+            ans.push(cur_vec.clone());
+            return;
+        }
+        for i in cur_index..candidates.len() {
+            cur_vec.push(candidates[i]);
+            Self::dfs(target, length, i + 1, cur_sum + candidates[i], cur_vec, candidates, ans);
+            cur_vec.pop().unwrap();
+        }
+    }
+}