[LeetCode] 20. Valid Parentheses (Easy)

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class Solution {
    public boolean isValid(String s) {
        Map<Character, Integer> patterns = new HashMap();
        Stack<Character> stack = new Stack<>();
        int sum = 0;

        patterns.put('(', 1);
        patterns.put(')', 2);
        patterns.put('{', 3);
        patterns.put('}', 4);
        patterns.put('[', 5);
        patterns.put(']', 6);

        if(s.length() % 2 == 1) return false;

        for(int i = 0; i < s.length(); i++, i++) {
            if(patterns.get(s.charAt(i)) % 2 == 1) {
                stack.push(s.charAt(i));
                // sum += patterns.get(s.charAt(i)).intValue() + 1;
            } else if(patterns.get(s.charAt(i)) % 2 == 0) {
                // sum -= patterns.get(s.charAt(i)).intValue();
                if(stack.isEmpty()) return false;
                Character temp = stack.pop();
                if(patterns.get(temp) + 1 != patterns.get(s.charAt(i))) return false;
            }
        }

        if(sum != 0) return false;

        return true;
    }
}

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class Solution {
    public boolean isValid(String s) {

        Stack<Character> stack = new Stack<>();

        for(char c : s.toCharArray()) {
            if(c == '(') stack.push(')');
            else if(c == '[') stack.push(']');
            else if(c == '{') stack.push('}');
            else if(stack.isEmpty()) return false;
            else if(stack.pop() != c) return false;
        }

        return stack.isEmpty();
    }
}

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else if(stack.isEmpty()) return false;

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else if(stack.pop() != c) return false;