【LeetCode】20. Valid Parentheses

最新推荐文章于 2024-02-05 23:11:57 发布

YolandaJia

最新推荐文章于 2024-02-05 23:11:57 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。该算法能正确判断括号是否成对出现且顺序正确，适用于多种编程场景。

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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

Solution:

Iterate the string, use a stack to push element with (, {, [, when element is ), }, or ], stack.pop() to see if popped on is corresponding to the element.

Code:

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