/**
     * brute force
     * T(n) = O(n^2)
     * S(n) = O(1);
     * @param nums
     * @param target
     * @return
     */
    public int[] twoSum(int[] nums, int target) {

        for (int i = 0; i<nums.length; i++) {
            for (int j=0; j<nums.length; j++) {
                if (nums[i] + nums[j] == target) {
                    return new int[] {i,j};
                }
            }
        }

        throw new IllegalArgumentException("nums should have one solution");
    }