Python Program:

Example:

A
A B
A B C

rows=int(input("Enter number of rows : "))
for i in range(1,rows+1):
  c=65
  for j in range(1,i+1):
    print(chr(c),end=" ")
    c+=1
  print("")

Output:

  Enter number of rows : 4
  A
  A B
  A B C
  A B C D

Main logic :

for i in range(1,rows+1): #rows : number of rows to print
  c=65  #"A" starts from 65
  for j in range(1,i+1):
    print(chr(c),end=" ")
    c+=1
  print("")

You can print the same pattern in small alphabets, just set c=97