update 0077.组合优化.md 关于 rust 的一些优化

problems/0077.组合优化.md

@@ -267,22 +267,22 @@ Rust:
 
 ```Rust
 impl Solution {
-    fn backtracking(result: &mut Vec<Vec<i32>>, path: &mut Vec<i32>, n: i32, k: i32, startIndex: i32) {
+    fn backtracking(result: &mut Vec<Vec<i32>>, path: &mut Vec<i32>, n: i32, k: i32, start_index: i32) {
         let len= path.len() as i32;
         if len == k{
             result.push(path.to_vec());
             return;
         }
 	// 此处剪枝
-        for i in startIndex..= n - (k - len) + 1 {
+        for i in start_index..= n - (k - len) + 1 {
             path.push(i);
             Self::backtracking(result, path, n, k, i+1);
             path.pop();
         }
     }
     pub fn combine(n: i32, k: i32) -> Vec<Vec<i32>> {
-        let mut result: Vec<Vec<i32>> = Vec::new();
-        let mut path: Vec<i32> = Vec::new();
+        let mut result = vec![];
+        let mut path = vec![];
         Self::backtracking(&mut result, &mut path, n, k, 1);
         result
     }