UNDECLARED MAJOR in UCI, UCSB, UCSD

I got accepted into UCSD (John Muir), UCI, and UCSB but I was placed as Undeclared Major in all schools.
How hard would it be to get into Computer Engineering or Computer Science as my major

UCSD very difficult: https://cse.ucsd.edu/undergraduate/cse-capped-major-status
UCSB “highly competitive”: https://engineering.ucsb.edu/undergraduate/academic-advising/change-major-college-engineering
UCI: http://changeofmajor.uci.edu/school-of-information-and-computer-sciences/#cgs and http://changeofmajor.uci.edu/engineering/#computer

UCSD is a lottery to get into the major. I would go for an direct admit options. UCI might be possible but not guaranteed. UCSB can be just as difficult as UCSD but it is not a lottery.

For UCSB:
Students who began as freshmen who plan to enter an engineering major or to change from one engineering major to another will be expected to complete at least 30 units at UCSB before petitioning for a change of major and usually must satisfy the prerequisites of the prospective major. Students who have completed more than 105 units will not be considered for a change of major/change of college in engineering or computer science unless they can demonstrate that they will be able to complete all the degree requirements without exceeding 215 total units.

Notwithstanding any of the major-specific requirements described below, we caution that the capacity of any given program to accept new students changes, sometimes substantially, from year to year. It is incumbent upon students to continue to make progress in a backup major while pursuing a new major in the College of Engineering, and to periodically consult academic advisors in both the desired major as well as the backup major regarding the viability of pursuing the change of major.
COMPUTER ENGINEERING

Students may petition to enter the Computer Engineering major at any time both of the following requirements are met:

An overall UCSB grade point average of at least 3.0.
Satisfactory completion at UCSB, with a grade point average of 3.0 or better, of any five classes, including at least two Electrical & Computer Engineering (ECE) classes and two Computer Science (CMPSC) classes, from the following: Math 4B or 5A, ECE 2A-B-C, ECE 15A, CMPSC 16, 24, 32, 40.
COMPUTER SCIENCE

Students may petition to enter the Computer Science major when
the following requirements are met:
A cumulative grade point average of at least 3.0;
Satisfactory completion of Computer Science 16 and 24 with a cumulative GPA of 3.2 or higher (first takes only);
Satisfactory completion of Math 3A, 3B, 4A, 4B and Computer Science 40 with a cumulative GPA of 3.0 or higher (first takes only)
The selection process is highly competitive and these milestones are minimum requirements for consideration, achieving them does not guarantee admission to the Computer Science major. Any petitions denied will be automatically considered a second time in the next quarter. Petitions denied a second time will not be reconsidered. Details found at the CS “Admission to the Major” page.

For UCI:
Computer Science
Requirements Description
Cumulative UC GPA Students must meet BOTH requirements:
Minimum of 2.7 GPA overall
Minimum GPA of 2.7 in the quarter immediately preceding the change of major
Course grades A minimum GPA of 3.0 and no grade less than a C in ALL courses taken from those listed below. Completion of the following:
ICS 31 and ICS 32, or
ICS 32A and ICS 33, and
One or more of Math 2A, Math 2B, ICS 6B, ICS 6D, ICS 6N
Other

90 units of less. Students with more than 90 units may not be admitted to the major; they will be reviewed on a case-by-case basis provided they have made substantial progress in courses required for the major.
Students must be in good academic standing.
Students must complete all change of major requirements at the time of application.
Student performance in coursework taken toward intended major’s degree requirements will be factored into consideration during change of major review and may result in denial of admission into the major.

Computer Science and Engineering
Requirements Description
Cumulative UC GPA 2.7 overall and 2.7 quarterly GPA in the quarter immediately preceding the change of major request.
Course grades Minimum 3.0 GPA in prerequisite courses:
Math 2A-B-D
Physics 7C-7D, 7LC-7LD
ICS 21-22 or CSE 31-32 or ICS 31-32 or CSE 41-42
Other

Students admitted to the major in Computer Science and Engineering will be assigned to the Donald Bren School of Information and Computer Sciences or The Henry Samueli School of Engineering based on enrollment.
Students with more than 90 units will be reviewed on a case-by-case basis, provided they have made substantial progress in courses required for the major.