Consider you are deciding among four hash functions (h1, h2, h3, h4) and the following keys:

key	12	34	45	58	67	78	85	88	95
h1(key)	2	4	5	8	7	8	5	8	5
h2(key)	5	6	6	2	4	1	1	4	4
h3(key)	3	7	3	2	4	6	4	7	5
h4(key)	4	2	0	0	3	6	5	0	7

a. Explain a criterion that measures the effectiveness of a hash function. Specify if you would like the criterion to be maximized or minimized.

b. Using the criterion, measure each hash function and indicate which hash function is more effective (indicate ties if any)