java - How do I find a recurrence relation for a recursive method? -

so i'm trying find recurrence relation java method:

public static pair min/max(int start, int end, int[] a) {         int mid;         pair pair = new pair(a[start], a[end]);         pair p1;         pair p2;          if (start == end) { //if n = 1             return pair;         }          else if (end == start + 1) { //if n = 2             if (a[start] > a[end]) {                 pair.upper = a[end];                 pair.lower = a[start];             } else {                 pair.upper = a[start];                 pair.lower = a[end];             }             return pair;         }          mid = (end + start) / 2; //if n > 2         p1 = min/max(end, mid, a);         p2 = min/max(mid + 1, ub, a);          if (p1.lower < p2.lower)             pair.upper = p1.lower;         else             pair.lower = p2.lower;          if (p1.upper > p2.upper)             pair.upper = p1.upper;         else             pair.upper = p2.upper;          return pair; //the min , max pair     } 

this supposed find max , min of array using ⌈3n/2 - 2⌉ comparisons. uses class:

class pair {    int lower;    int upper;    pair ( int a, int o ) { lower = a; upper = o; } } 

so recurrence relation method? know starts out as:

c(n) = 0 if n=1        1 if n=2 

and i'm trying figure out equation when n > 2. first off above method run in ⌈3n/2 - 2⌉ comparisons. i'm wondering because of line mid = (lb + ub) / 2 makes me think i'm still splitting array ⌈n/2⌉ , ⌊n/2⌋ parts not me ⌈3n/2 - 2⌉ comparisons each time. know there better way same thing code i'm writing has use recursion.

update: after adding counter statements find above code not use ⌈3n/2 - 2⌉ comparisons every array. think problem variable mid. mid i'm supposed split array don't think i'm splitting correctly have proper number of comparisons.

let n = end - start + 1. presume mean recurrence expressing number of comparisons.

in general case doing 4 comparisons each level of recursion , splitting list in half. recurrence is:

t(n) = 4 + t( floor(n/2) ) + t( ceiling(n/2) ) n > 1 

nb: seem have begun lb , ub , switched partially start , end.