添加了0509.斐波那契数列Rust两种解法的代码

problems/0509.斐波那契数.md

@@ -277,7 +277,30 @@ int fib(int n){
     return fib(n-1) + fib(n-2);
 }
 ```
+### Rust
+动态规划:
+```Rust
+pub fn fib(n: i32) -> i32 {
+    let n = n as usize;
+    let mut dp = vec![0; 31];
+    dp[1] = 1;
+    for i in 2..=n {
+        dp[i] = dp[i - 1] + dp[i - 2];
+    }
+    dp[n]
+}
+```
 
-
+递归实现：
+```Rust
+pub fn fib(n: i32) -> i32 {
+    //若n小于等于1，返回n
+    f n <= 1 {
+        return n;
+    }
+    //否则返回fib(n-1) + fib(n-2)
+    return fib(n - 1) + fib(n - 2);
+}
+```
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