PPractick

The problem

In this triangle every row ends on the same letter, the n-th letter of the alphabet, and each row starts one letter earlier than the one above it. For n = 5, the rows are E, DE, CDE, BCDE, ABCDE. Compared with Pattern 15, which always starts at A and stops earlier, this one always stops at the same letter and starts earlier. That's a useful twist because the starting letter has to be computed from both n and the row.

Example for n = 5:

E
DE
CDE
BCDE
ABCDE

Function signature

vector<string> alphaTriangle(int n);  // row i: letters from the (n - i + 1)-th to the n-th

Test cases

Input n	Output rows	Explanation
1	"A"	The 1st letter is A
3	"C", "BC", "ABC"	Every row ends in C
5	"E", "DE", "CDE", "BCDE", "ABCDE"	Every row ends in E

(Confirm: 1 ≤ n ≤ 26; letters without separators.)

How interviewers phrase it

• "Print the alpha triangle: E, DE, CDE, BCDE, ABCDE for N = 5."
• "Print a triangle where each row ends with the N-th letter."

Clarifying questions to ask

1. N at most 26?
2. Separators between letters?
3. Print or return?

Follow-ups to expect

1. "What's the first letter of row i?"
2. "How is this different from Pattern 15?"
3. "Complexity?"

Related questions

• Easy and Medium Easy
• Hard Easy
• Pattern 1 Easy
• Pattern 2 Easy
• Pattern 3 Easy
• Pattern 4 Easy

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