Consider the basic block given below.

a = b + c 
c = a + d 
d = b + c 
e = d - b 
a = e + b

The minimum number of nodes and edges present in the DAG representation of the above basic block respectively are

The program below uses six temporary variables a, b, c, d, e, f.

a = 1 
b = 10 
c = 20 
d = a + b 
e = c + d 
f = c + e 
b = c + e 
e = b + f 
d = 5 + e 
return d + f

Assuming that all operations take their operands from registers, what is the minimum number of registers needed to execute this program without spilling?