Exercise $1-$ Pattern

$(20$ pts solution $+10$ points tracing$)$

Write a program which reads as input a natural number $n$ and then prints a "triangle like pattern" with letters as it is shown below. The height of the triangle $($number of rows$)$ will be $n.$ Trace the code $($show how the value of the variables change for each iteration$)$ for an input greater than $3.$

If the input is $7,$ the output is as follows:

A

B C

DEF

GHIJ

KLMNO

PQRSTU

VWXYZAB