Search for a range

    public int[] searchRange(int[] nums, int target) {
        if ( nums == null || nums.length == 0 ) 
            return new int[]{-1, -1};

        // first position
        int start = 0 ;
        int end = nums.length - 1;
        int[] bound = new int[2];
        while ( start + 1 < end ){
            int mid = start + (end - start) / 2;
            if ( nums[mid] < target){
                start = mid;
            }else {
                end = mid;
            }
        } 
        if ( nums[start] == target) bound[0] = start;
        else if (nums[end] == target) bound[0] = end;
        else return new int[]{-1, -1};

       //last position
        start = 0 ;
        end = nums.length - 1; 
        while ( start + 1 < end ){
            int mid = start + (end - start) / 2;
            if ( nums[mid] > target){
                end = mid;
            }else {
                start = mid;
            }
        } 
        if ( nums[end] == target) bound[1] = end;
        else if (nums[start] == target) bound[1] = start;
        else return new int[]{-1, -1};
        return bound;
}