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Leetcode020-validParentheses

Posted on Edited on In Views: Valine:
Solution Report of LeetCode Acceptted

Description

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

Example 1:

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Input: "()"
Output: true

Example 2:
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Input: "()[]{}"
Output: true

Example 3:
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Input: "(]"
Output: false

Example 4:
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Input: "([)]"
Output: false

Example 5:
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Input: "{[]}"
Output: true

Solution

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class Solution {
    public boolean isValid(String s) {
        if(s == null || s.length() == 0) return true;
        Stack<Character> st = new Stack<>();
        for (char ch: s.toCharArray()){
            if (ch == '(' || ch == '[' || ch == '{') st.push(ch);
            else switch (ch){
                case ')':
                    if (st.isEmpty() || st.pop() != '(')
                        return false;
                    break;
                case ']':
                    if (st.isEmpty() || st.pop() != '[')
                        return false;
                    break;
                case '}':
                    if (st.isEmpty() || st.pop() != '{')
                        return false;
                    break;
            }
        }
        if (!st.isEmpty()) return false;
        return true;
    }
}