A right-aligned number triangle prints 1 to i on row i, with leading spaces so shorter rows sit against the right edge.
Rule: spaces while j > i, then print 1..i with width 2
1
1 2
1 2 3
1 2 3 4
1 2 3 4 5 ← rows = 5Follows the hollow square border in Program 42; next is the diamond number pyramid in Program 44.
One outer row loop, a space loop for indent, then an ascending number loop with :2d.
| Method | Idea | Best for |
|---|---|---|
| Right-aligned | Spaces while j > i, then :2d for 1..i | Learning, interviews, exams |
| Rows input | Same logic with a user-chosen rows | Practice / demos |
for i from 1 to rows:
for j from rows down to i+1:
print one space
for k from 1 to i:
print k (width 2)
print newline| Goal | Pattern |
|---|---|
| Walk rows | for i in range(1, rows + 1): |
| Leading spaces | for j in range(rows, i, -1): print(" ", end="") |
| Print 1..i | for k in range(1, i + 1): print(f"{k:2d}", end="") |
| End the row | print() |
| API | Effect | Use for |
|---|---|---|
print(" ", end="") / print(f"{k:2d}", end="") | Stays on the same line | Each space or number |
print() | Ends the current line | After both inner loops |
Print spaces and numbers without a newline, then end the row once.
Change the row count and the right-aligned triangle updates instantly.
rows = 4Trace spaces and the ascending sequence on each row.
i | Spaces / numbers | Printed row |
|---|---|---|
1 | 3 spaces / 1 | 1 |
2 | 2 spaces / 1 2 | 1 2 |
3 | 1 space / 1 2 3 | 1 2 3 |
4 | none / 1 2 3 4 | 1 2 3 4 |
Space count = rows − i. Total numbers for n rows = n(n+1)/2.
Three complete programs: fixed 5 rows, input() rows, and a left-aligned contrast. Use View Output for sample results.
rows = 5Space loop for indent, then print 1..i with width 2.
rows = 5
for i in range(1, rows + 1):
for j in range(rows, i, -1):
print(" ", end="")
for k in range(1, i + 1):
print(f"{k:2d}", end="")
print()1. Outer loop. i runs from 1 to 5 — one row per value of i.
2. Indent. Print one space while j runs from rows down past i.
3. Numbers. Print k from 1 to i with f"{k:2d}", then end the line.
Read the row count with input() and build the same right-aligned triangle.
try:
rows = int(input("Enter number of rows: "))
except ValueError:
print("Please enter a positive whole number.")
raise SystemExit(1)
if rows < 1:
print("Please enter a positive whole number.")
raise SystemExit(1)
for i in range(1, rows + 1):
for j in range(rows, i, -1):
print(" ", end="")
for k in range(1, i + 1):
print(f"{k:2d}", end="")
print()1. Validate rows. Catch ValueError; require rows >= 1.
2. Same triangle. Only the bound changes from the literal 5 to the user value.
3. Safer input tip. Cap demos for readable output:
if rows < 1 or rows > 9:
print("Enter a whole number from 1 to 9.")
raise SystemExit(1)Skip the space loop — numbers start at the left margin.
rows = 5
for i in range(1, rows + 1):
for k in range(1, i + 1):
print(f"{k:2d}", end="")
print()1. No indent. Without the space loop, every row starts at column 0.
2. Same numbers. f"{k:2d}" still keeps digit columns stable.
3. Compare. Place this next to Example 1 to see what the space loop contributes.
Check these before calling the solution done.
The triangle snaps left. Keep for j in range(rows, i, -1) for right alignment.
print(k, end="")Columns drift once values hit two digits. Prefer f"{k:2d}".
print() inside an inner loopEach space or number lands on its own line. End the row only after both loops.
Output is just the formatted 1 — no leading spaces.
ValueErrorBare int(input()) crashes on non-numeric text — wrap it in try/except ValueError.
" "This pattern uses one space per indent step plus :2d on numbers. Two-space indents over-shift the triangle.
| Program | Time | Extra space |
|---|---|---|
| Fixed / left-aligned (Examples 1, 3) | O(n²) | O(1) |
| User input (Example 2) | O(n²) | O(1) |
Total printed numbers are 1 + 2 + … + n = n(n+1)/2, so work is quadratic in the row count.
j > i, then print 1..i with :2d.rows − i; width-2 keeps digits in columns.print() advances after each row.O(n²) time; O(1) extra space.One line: indent with spaces, then print 1 to i with fixed width on each row.
Each row prints numbers 1 to i. A space loop runs while j > i before the number loop; f"{k:2d}" keeps columns aligned. Total prints = n(n+1)/2.
Continue with a centered diamond of ascending digit sequences.
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