[LeetCode]--20. Valid Parentheses

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

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

public boolean isValid(String s) {
        if (s.length() % 2 != 0)
            return false;
        char[] characters = new char[s.length()];
        int index = 0, i;
        for (i = 0; i < s.length(); i++) {
            if (s.charAt(i) == '(')
                characters[index++] = s.charAt(i);
            if (s.charAt(i) == '[')
                characters[index++] = s.charAt(i);
            if (s.charAt(i) == '{') {
                characters[index++] = s.charAt(i);
                System.out.println(index);
            }

            if (s.charAt(i) == ')') {
                if (--index < 0 || characters[index] != '(')
                    break;
            }
            if (s.charAt(i) == ']') {
                if (--index < 0 || characters[index] != '[')
                    break;
            }
            if (s.charAt(i) == '}') {
                if (--index < 0 || characters[index] != '{')
                    break;
            }
        }
        if (i == s.length() && index == 0)
            return true;
        return false;
    }

方法通过了，不过觉得有点笨，暂时也没想到好的，先就这样啦。LeedCode也没给我们提供详解。

找到一个写得比较好的程序，极力推荐大家不要看我的，看这个，又感觉被甩了几条街。

public boolean isValidParentheses(String s) {
        Stack<Character> stack = new Stack<Character>();
        for (Character c : s.toCharArray()) {
        if ("({[".contains(String.valueOf(c))) {
                stack.push(c);
            } else {
               if (!stack.isEmpty() && is_valid(stack.peek(), c)) {
                   stack.pop();
               } else {
                   return false;
               }
           }
       }
       return stack.isEmpty();
    }

    private boolean is_valid(char c1, char c2) {
        return (c1 == '(' && c2 == ')') || (c1 == '{' && c2 == '}')
            || (c1 == '[' && c2 == ']');
    }

用了系统的栈，我用的数组栈。