Update 0509.斐波那契数.md

problems/0509.斐波那契数.md

@@ -347,26 +347,32 @@ int fib(int n){
 ### 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];
+impl Solution {
+    pub fn fib(n: i32) -> i32 {
+        if n <= 1 {
+            return n;
+        }
+        let n = n as usize;
+        let mut dp = vec![0; n + 1];
+        dp[1] = 1;
+        for i in 2..=n {
+            dp[i] = dp[i - 2] + dp[i - 1];
+        }
+        dp[n]
     }
-    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;
+impl Solution {
+    pub fn fib(n: i32) -> i32 {
+        if n <= 1 {
+            n
+        } else {
+            Self::fib(n - 1) + Self::fib(n - 2)
+        }
     }
-    //否则返回fib(n-1) + fib(n-2)
-    return fib(n - 1) + fib(n - 2);
 }
 ```