PPractick

The problem

In this triangle the numbers keep counting across rows: row 1 has 1, row 2 has 2 3, row 3 has 4 5 6, and so on. It's known as Floyd's triangle. Unlike Patterns 3 and 4, the printed value depends on neither the row nor the column alone, but on how many numbers have been printed so far. The natural solution is a counter that lives outside both loops.

Example for n = 4:

1
2 3
4 5 6
7 8 9 10

Function signature

vector<string> floydTriangle(int n);  // row i has i consecutive numbers continuing from the previous row

Test cases

Input n	Output rows	Explanation
1	"1"
3	"1", "2 3", "4 5 6"	The counter carries over between rows
4	"1", "2 3", "4 5 6", "7 8 9 10"	Last number is n(n + 1) / 2 = 10
5	last row "11 12 13 14 15"	Two-digit numbers, still space-separated

(Confirm: space-separated with no trailing space.)

How interviewers phrase it

• "Print Floyd's triangle for N rows."
• "Print numbers 1, 2, 3, ... in a triangle where row i has i numbers."

Clarifying questions to ask

1. Space-separated?
2. How large can N be? (The last number is n(n + 1) / 2.)
3. Print or return?

Follow-ups to expect

1. "Why declare the counter outside the loops?"
2. "What's the first number of row i without a counter?"
3. "What's the last number printed?"
4. "What's the complexity?"

Related questions

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

All 474 dsa interview questions

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