t1 and t2 divide array passed to the function into 3 parts.
low to t1 is first 1/3rd part, t1 to t2 second 1/3rd part and t2 to hight last 1/3rd
Note that:
Low to t2 is 2/3rd
t1 to high is 2/3rd
T(n)=3T(2n/3)+O(1)
Using masters theorem
a=3, b=3/2
T(n)=Thetha(nlogba)=Thetha(n2.7095112913514545)