Saturday, February 6, 2016

Valid Parentheses

Valid Parentheses

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

Example

The brackets must close in the correct order, "()" and "()[]{}" are all valid but "(]" and "([)]" are not.


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public class Solution {
    /**
     * @param s A string
     * @return whether the string is a valid parentheses
     */
    public boolean isValidParentheses(String s) {
        // Write your code here
        Stack<Character> stack = new Stack<Character>();
        
        for (int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);
            switch (c) {
                case '(':
                    stack.push(c);
                    break;
                case '[':
                    stack.push(c);
                    break;
                case '{':
                    stack.push(c);
                    break;
                case ')':
                    if (stack.isEmpty() || stack.pop() != '(') {
                        return false;
                    }
                    break;
                case ']':
                    if (stack.isEmpty() || stack.pop() != '[') {
                        return false;
                    }
                    break;
                case '}':
                    if (stack.isEmpty() || stack.pop() != '{') {
                        return false;
                    }
                    break;
                default:
                    break;
            }
        }
        
        if (stack.isEmpty()) {
            return true;
        }
        else {
            return false;
        }
    }
}
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