leetcode 20. valid parentheses

20. Valid Parentheses

Difficulty:: Easy

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:

1 2	Input: "()" Output: true

Example 2:

1 2	Input: "()[]{}" Output: true

Example 3:

1 2	Input: "(]" Output: false

Example 4:

1 2	Input: "([)]" Output: false

Example 5:

1 2	Input: "{[]}" Output: true

Solution

Language: Java

class  {
    public boolean isValid(String s) {
        if (s == null || s.length() == 0) {
            return true;
        }
        Deque<Character> stack = new ArrayDeque<>();
        for (int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);
            switch(c) {
                case '(':
                    stack.push(')');
                    break;
                case '[':
                    stack.push(']');
                    break;
                case '{':
                    stack.push('}');
                    break;
                default:
                    if (stack.isEmpty()) {
                        return false;
                    } else if (stack.peek() == c) {
                        stack.pop();
                    } else {
                        return false;
                    }
            }
        }
        return stack.isEmpty();
    }
}

也可以考虑用数组作为栈

leetcode 20. valid parentheses

20. Valid Parentheses

Solution

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