20 Valid Parentheses

最新推荐文章于 2020-01-22 13:03:47 发布

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本文介绍了一种使用栈数据结构来验证包含括号的字符串是否有效的算法。该算法确保每种类型的左括号都能被相应的右括号正确闭合，并且遵循正确的闭合顺序。通过几个示例展示了算法的有效性和准确性。

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

An input string is valid if:

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

Note that an empty string is also considered valid.

Example 1:

Input: "()"
Output: true

Example 2:

Input: "()[]{}"
Output: true

Example 3:

Input: "(]"
Output: false

Example 4:

Input: "([)]"
Output: false

Example 5:

Input: "{[]}"
Output: true

class Solution {
    public boolean isValid(String s) {
        if (s.length() % 2 != 0)
            return false;
        
        Stack<Character> stack = new Stack<>();
        for (char c : s.toCharArray()) {
            if (c == '(')
                stack.push(')');
            else if (c == '{')
                stack.push('}');
            else if (c == '[')
                stack.push(']');
            else if (stack.isEmpty() || stack.pop() != c)
                return false;
        }
        
        return stack.isEmpty();
    }
}