LeetCode-in-All

20. Valid Parentheses

Easy

Given a string s containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.

An input string is valid if:

1. Open brackets must be closed by the same type of brackets.
2. Open brackets must be closed in the correct order.

Example 1:

Input: s = “()”

Output: true

Example 2:

Input: s = “()[]{}”

Output: true

Example 3:

Input: s = “(]”

Output: false

Example 4:

Input: s = “([)]”

Output: false

Example 5:

Input: s = “{[]}”

Output: true

Constraints:

• 1 <= s.length <= 104
• s consists of parentheses only '()[]{}'.

Solution

impl Solution {
    pub fn is_valid(s: String) -> bool {
        let mut stack = Vec::new();
        for c in s.chars() {
            match c {
                '(' | '[' | '{' => stack.push(c),
                ')' => {
                    if stack.is_empty() || stack.pop() != Some('(') {
                        return false;
                    }
                }
                '}' => {
                    if stack.is_empty() || stack.pop() != Some('{') {
                        return false;
                    }
                }
                ']' => {
                    if stack.is_empty() || stack.pop() != Some('[') {
                        return false;
                    }
                }
                _ => return false,
            }
        }

        stack.is_empty()
    }
}

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