diff --git a/problems/0738.单调递增的数字.md b/problems/0738.单调递增的数字.md
index f92652cd..1cf8a0a6 100644
--- a/problems/0738.单调递增的数字.md
+++ b/problems/0738.单调递增的数字.md
@@ -280,18 +280,20 @@ object Solution {
 ```Rust
 impl Solution {
     pub fn monotone_increasing_digits(n: i32) -> i32 {
-        let mut str_num = n.to_string().chars().map(|x| x.to_digit(10).unwrap() as i32).collect::<Vec<i32>>();
-        let mut flag = str_num.len();
-        for i in (1..str_num.len()).rev() {
-            if str_num[i - 1] > str_num[i] {
+        let mut n_bytes = n.to_string().into_bytes();
+        let mut flag = n_bytes.len();
+        for i in (1..n_bytes.len()).rev() {
+            if n_bytes[i - 1] > n_bytes[i] {
                 flag = i;
-                str_num[i - 1] -= 1;
+                n_bytes[i - 1] -= 1;
             }
         }
-        for i in flag..str_num.len() {
-            str_num[i] = 9;
+        for v in n_bytes.iter_mut().skip(flag) {
+            *v = 57;
         }
-        str_num.iter().fold(0, |acc, x| acc * 10 + x)
+        n_bytes
+            .into_iter()
+            .fold(0, |acc, x| acc * 10 + x as i32 - 48)
     }
 }
 ```