class Solution {
    public int[] twoSum(int[] nums, int target) {
        Map<Integer, Integer> map = new HashMap<>();
        for (int i = 0; i < nums.length; ++i) {
            map.put(nums[i], i);
        }
        for (int i = 0; i < nums.length; ++i) {
            int cur = nums[i];
            int second = target - cur;
            if (map.containsKey(second) && map.get(second) != i) {
                return  new int[]{i, map.get(second)};
            }
        }
        return new int[]{};
    }
}

                

class Solution {
    private static Map<Character, Character> map = Map.of(
            '[', ']',
            '(', ')',
            '{', '}'
        );

    public boolean isValid(String s) {
        Stack<Character> stack = new Stack<>();
        for (char c : s.toCharArray()) {
            if (map.containsKey(c)) {
                stack.push(c);
            } else {
                if (stack.isEmpty()) return false;
                if (c != map.get(stack.pop())) return false;
            }
        }

        return stack.isEmpty();
    }
}