update 0020.有效的括号.md about rust

problems/0020.有效的括号.md

@@ -493,6 +493,33 @@ object Solution {
 }
 ```
 
+rust:
+
+```rust
+impl Solution {
+    pub fn is_valid(s: String) -> bool {
+        if s.len() % 2 == 1 {
+            return false;
+        }
+        let mut stack = vec![];
+        let mut chars: Vec<char> = s.chars().collect();
+        while let Some(s) = chars.pop() {
+            match s {
+                ')' => stack.push('('),
+                ']' => stack.push('['),
+                '}' => stack.push('{'),
+                _ => {
+                    if stack.is_empty() || stack.pop().unwrap() != s {
+                        return false;
+                    }
+                }
+            }
+        }
+        stack.is_empty()
+    }
+}
+```
+
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