An increasing triangle from 0 uses zero-based loops — each cell is i + j, so the first row is 0 and row i starts at i.
Rule: for i = 0..maxN
for j = 0..i
print (i + j) + " "
0
1 2
2 3 4
3 4 5 6
4 5 6 7 8
5 6 7 8 9 10 ← maxN = 5Twin of Program 33 (i + j - 1 from 1): same growing shape, but both loops start at 0.
Walk i from 0 to maxN; on each row append i + 1 values using i + j.
| Method | Idea | Best for |
|---|---|---|
| Nested loops | Outer i = 0..maxN; inner j = 0..i; value i + j | Learning, interviews |
| prompt maxN | Same loops; read max index at runtime | Interactive practice |
| Compact maxN = 2 | Same formula; easier to trace by hand | Paper walkthrough |
for i from 0 to maxN:
line = ""
for j from 0 to i:
line += (i + j) + " "
print line (with newline)| Goal | Pattern |
|---|---|
| Set max index | const maxN = 5; |
| Outer loop | for (let i = 0; i <= maxN; i++) |
| Inner loop | for (let j = 0; j <= i; j++) |
| Value | line += (i + j) + " "; |
| End row | console.log(line); |
| Row length | i + 1 values |
| vs Program 33 | i + j - 1 with i from 1 |
| API | Effect | Use for |
|---|---|---|
line += value + " " | Stays on the same row | Each number |
console.log(line) | Ends the line | After the inner loop |
Build the row with +=, then break once with console.log. Putting console.log inside the inner loop prints one number per line.
Change the max index and the triangle from 0 updates instantly.
maxN = 2Trace each outer i, the formula i + j, and the printed row.
i | Values i+j | Printed row |
|---|---|---|
0 | 0+0 = 0 | 0 |
1 | 1, 2 | 1 2 |
2 | 2, 3, 4 | 2 3 4 |
Each next row starts at i and adds one more consecutive value — total rows = maxN + 1.
Three complete programs: fixed maxN = 5, prompt max index, and compact maxN = 2. Use View Output for sample results, or Try It Yourself to edit and run in the playground.
maxN = 5Hard-coded max index — zero-based nested loops with formula i + j.
const maxN = 5;
for (let i = 0; i <= maxN; i++) {
let line = "";
for (let j = 0; j <= i; j++) {
line += (i + j) + " ";
}
console.log(line);
}1. Outer loop. i runs from 0 to 5 — six rows total.
2. Inner loop. j runs from 0 to i; append (i + j) + " ".
3. Newline. console.log(line) after the inner loop prints the row.
Read maxN at runtime; allow 0 as a valid minimum.
const maxN = parseInt(prompt("Enter max i:"), 10);
if (!Number.isFinite(maxN) || maxN < 0) {
console.log("Please enter a non-negative integer.");
} else {
for (let i = 0; i <= maxN; i++) {
let line = "";
for (let j = 0; j <= i; j++) {
line += (i + j) + " ";
}
console.log(line);
}
}1. Prompt and parse. Convert the answer with parseInt(..., 10).
2. Validate first. Reject NaN or negative values — 0 is allowed.
3. Same loops. Only the source of maxN changes — still print i + j on each row.
maxN = 2Same nested-loop formula with a smaller max — easy to trace on paper.
const maxN = 2;
for (let i = 0; i <= maxN; i++) {
let line = "";
for (let j = 0; j <= i; j++) {
line += (i + j) + " ";
}
console.log(line);
}1. Same structure. Outer and inner loops match Example 1.
2. Only maxN changes. Three rows; total values = 1+2+3 = 6.
3. Trace first. Walk i = 0, 1, 2 on paper before scaling to 5 or more.
Check these before calling the solution done.
If console.log is inside the inner loop, each value lands on its own line. Log only after the row is built.
Starting i at 1 skips the 0 row and looks like Program 33 without the - 1.
Use j <= i so row i prints i + 1 values. j < i drops the last cell.
Output is just 0 — valid and useful for testing input handling.
Omitting + " " prints 12 instead of 1 2.
Letters or empty prompt yield NaN — check Number.isFinite(maxN) && maxN >= 0.
| Program | Time | Extra space |
|---|---|---|
| Examples 1–3 | O(n²) | O(n) for the current line string |
For max index n, rows = n + 1 and total values = 1 + 2 + … + (n+1) = (n+1)(n+2)/2 → O(n²).
i + j for j = 0..i with i from 0 to maxN.0; row length is i + 1.line += … builds; console.log(line) breaks.O(n²) for max index n.One line: start both loops at 0 and print i + j to grow a triangle that begins with zero.
Each printed value is computed as i + j. With i = 0 and j = 0 the first row prints 0; row i = 2 prints 2, 3, 4 — a zero-based left-shifted increasing triangle.
Continue with the next pattern in the JavaScript number-pattern series.
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