A reverse descending triangle shortens each row from the top — 54321, 4321, 321, 21, 1 — with digits counting down on every line.
Rule: for i = rows down to 1
print digits i..1
54321
4321
321
21
1 ← rows = 5After Program 2’s left-shifted i..n rows, this one flips both loops downward so each row reads in reverse.
Count i down from rows; on each row, print digits from i down to 1.
| Method | Idea | Best for |
|---|---|---|
| Nested loops | Outer i = rows..1; inner j = i..1 | Learning, interviews |
| input() rows | Same loops; read rows at runtime | Interactive practice |
| Spaced digits | print(j, end=" ") | Readable output |
for i from rows down to 1:
for j from i down to 1:
print j (same line)
print newline| Goal | Pattern |
|---|---|
| Set size | rows = 5 |
| Outer loop | for i in range(rows, 0, -1): |
| Inner loop | for j in range(i, 0, -1): print(j, end="") |
| End row | print() |
| Digits printed | i..1 (length i) |
| Spaced | print(j, end=" ") |
| API | Effect | Use for |
|---|---|---|
print(j, end="") | Stays on the same line | Each digit |
print() | Ends the current line | After the inner loop |
Glue digits with end="", then break once with print(). Putting print() inside the inner loop prints one digit per line.
Change the row count and the reverse descending triangle updates instantly.
rows = 3Trace each outer value of i and the digits printed from i down to 1.
i | Digits i..1 | Printed row |
|---|---|---|
3 | 3 2 1 | 321 |
2 | 2 1 | 21 |
1 | 1 | 1 |
As i falls, the inner loop starts lower — one fewer digit each row.
Three complete programs: fixed rows = 5, input() rows, and spaced digits. Use View Output for sample results.
rows = 5Hard-coded height — outer shrinks the row; inner prints digits in reverse.
rows = 5
for i in range(rows, 0, -1):
for j in range(i, 0, -1):
print(j, end="")
print()1. Outer loop. i runs from 5 down to 1 — the starting digit and row length.
2. Inner loop. j runs from i down to 1, so print(j, end="") builds i..1.
3. Newline. print() after the inner loop ends the row and starts the next one.
Read rows at runtime with input() and int().
rows = int(input("Enter the number of rows: "))
if rows < 1:
print("Please enter a positive integer.")
else:
for i in range(rows, 0, -1):
for j in range(i, 0, -1):
print(j, end="")
print()1. Read and validate. Parse the answer; reject non-positive values before looping.
2. Same loops. Only the source of rows changes — still print i..1 on each row.
3. Safer input tip. Bare int(input()) raises ValueError on letters. Prefer:
raw = input("Enter the number of rows: ").strip()
try:
rows = int(raw)
except ValueError:
print("Please enter a positive integer.")
raise SystemExit(1)
if rows < 1:
print("Please enter a positive integer.")
raise SystemExit(1)Keep rows = 5 but print a space after each digit.
rows = 5
for i in range(rows, 0, -1):
for j in range(i, 0, -1):
print(j, end=" ")
print()1. Same structure. Outer and inner bounds match Example 1.
2. Only end= changes. Use print(j, end=" ") instead of print(j, end="").
3. Same shape. Values and row count stay the same — only spacing differs.
Check these before calling the solution done.
If print() is inside the inner loop, each digit lands on its own line. Use end=""; call bare print() only after the inner loop.
Using for j in range(1, i + 1) with a descending outer loop yields 12345, 1234, … — not this pattern.
Printing i instead of j repeats the row digit, not a countdown.
Output is just 1 on one line.
The outer loop never runs. Guard input() with rows >= 1.
Letters crash bare int(input()) — wrap in try/except and require rows >= 1.
| Program | Time | Extra space |
|---|---|---|
| Examples 1–3 | O(n²) | O(1) |
Total digits = n + (n−1) + … + 1 = n(n+1)/2 → O(n²).
i = rows..1; inner prints i..1.print() advances after each row.O(n²) for n rows.One line: shrink the outer count while the inner loop prints each row backwards from i to 1.
This pattern prints each row in descending order from i down to 1. The outer loop shrinks the row length while the inner loop counts downward — producing 54321, 4321, 321, and so on.
Continue with the next pattern in the Python number-pattern series.
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