public int search(int[] nums, int target) {
        if (nums == null) return -1;
        int low = 0, high = nums.length - 1;
        while (low <= high) {
            int mid = low + (high - low) / 2;
            if (nums[mid] == target) {
                return mid;
            // right half is sorted
            } else if (nums[low] > nums[mid]) {
                if (target > nums[mid] && target <= nums[high]) {
                    low = mid + 1;
                } else {
                    high = mid - 1;
                }
            // left half is sorted
            } else {
                if (target >= nums[low] && target < nums[mid]) {
                    high = mid - 1;
                } else {
                    low = mid + 1;
                }
            }
        }
        return -1;
    }