Let’s break everything down:

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🔁 Pattern Printing in JavaScript – Deep Dive

We use nested loops.

• Outer loop (i) → rows

• Inner loop (j, k) → columns (how many things to print per row)

• Conditions (i < n, j < n, etc.) decide when loops stop.

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1️⃣ Square of Stars

let n = 4;
for (let i = 0; i < n; i++) {    // row control
  let row = "";
  for (let j = 0; j < n; j++) {  // column control
    row += "*";
  }
  console.log(row);
}

🔹 Logic

• Outer loop → runs n times → total rows = 4

• Inner loop → also runs n times → total stars = 4 per row

🔹 Conditions

• i < n ensures loop runs exactly 4 rows.

• j < n ensures 4 stars are added per row.

✅ Output:

****
****
****
****

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2️⃣ Right Triangle of Stars

for (let i = 0; i < n; i++) {  
  let row = "";
  for (let j = 0; j < i + 1; j++) {  
    row += "*";
  }
  console.log(row);
}

🔹 Logic

• Outer loop: i=0..n-1 (row count)

• Inner loop: runs i+1 times → row length grows each time

🔹 Conditions

• Row 0 → j < 1 → 1 star

• Row 1 → j < 2 → 2 stars

• Row 2 → j < 3 → 3 stars

• Row 3 → j < 4 → 4 stars

✅ Output (n=4):

*
**
***
****

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3️⃣ Number Triangle (1..j)

for (let i = 0; i < n; i++) {
  let row = "";
  for (let j = 0; j <= i; j++) {
    row += (j + 1);
  }
  console.log(row);
}

🔹 Logic

• Outer loop → row count = n

• Inner loop → runs from 0 → i (inclusive)

• Prints numbers 1 to (i+1)

🔹 Conditions

• j <= i means row length = i+1

• Each row starts from j=0 so (j+1) gives 1,2,3,…

✅ Output (n=5):

1
12
123
1234
12345

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4️⃣ Number Triangle (Row number repeated)

for (let i = 0; i < n; i++) {
  let row = "";
  for (let j = 0; j <= i; j++) {
    row += (i+1);
  }
  console.log(row);
}

🔹 Logic

• Outer loop → row count = n

• Inner loop → runs i+1 times

• Instead of j+1, we use (i+1) → repeats row number

🔹 Conditions

• Row 0 → j=0..0 → prints 1

• Row 1 → j=0..1 → prints 22

• Row 2 → j=0..2 → prints 333

✅ Output:

1
22
333
4444
55555

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5️⃣ Inverted Number Triangle

for (let i = 0; i < n; i++) {
  let row = "";
  for (let j = 0; j < n-i; j++) {
    row += (j + 1);
  }
  console.log(row);
}

🔹 Logic

• Outer loop → controls row count

• Inner loop → length = n-i (shrinks each row)

🔹 Conditions

• Row 0 → j < 5 → 12345

• Row 1 → j < 4 → 1234

• Row 2 → j < 3 → 123

• Row 3 → j < 2 → 12

• Row 4 → j < 1 → 1

✅ Output:

12345
1234
123
12
1

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6️⃣ Inverted Triangle of Stars

for (let i = 0; i < n; i++) {
  let row = "";
  for (let j = 0; j < n-i; j++) {
    row += "*";
  }
  console.log(row);
}

🔹 Logic

• Same as previous but prints stars instead of numbers.

🔹 Conditions

• j < n-i → decreases star count each row.

✅ Output (n=5):

*****
****
***
**
*

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7️⃣ Right-Aligned Triangle (with spaces _)

for (let i = 0; i < n ; i++) {
  let row = "";
  for (let j = 0; j < n-(i+1); j++) {
    row += "_";   // spaces
  }
  for (let k = 0; k < i + 1; k++) {
    row += "*";
  }
  console.log(row);
}

🔹 Logic

• First inner loop → prints spaces _

• Second inner loop → prints stars *

• Spaces decrease, stars increase per row

🔹 Conditions

• Row 0 → spaces=4, stars=1

• Row 1 → spaces=3, stars=2

• Row 2 → spaces=2, stars=3

• Row 3 → spaces=1, stars=4

• Row 4 → spaces=0, stars=5

✅ Output:

____*
___**
__***
_****
*****

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8️⃣ Binary Triangle (Row-wise toggle reset)

for (let i = 0; i < n; i++) {
  let row = "";
  let toggle = 1;
  for (let j = 0; j <= i; j++) {
    row += toggle;
    toggle = toggle === 1 ? 0 : 1;
  }
  console.log(row);
}

🔹 Logic

• toggle starts at 1 fresh each row

• Flips between 1 → 0 → 1 → 0 …

🔹 Conditions

• Inner loop j <= i → row length grows

• Each iteration flips toggle

✅ Output:

1
10
101
1010
10101

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9️⃣ Binary Triangle (Global toggle continues across rows)

let toggle = 1;
for (let i = 0; i < n; i++) {
  let row = "";
  for (let j = 0; j <= i; j++) {
    row += toggle;
    toggle = toggle === 1 ? 0 : 1;
  }
  console.log(row);
}

🔹 Logic

• Global toggle → does not reset row by row

• Pattern continues across all rows

🔹 Conditions

• j <= i → row length increases

• Toggle value continues from previous row

✅ Output:

1
01
010
1010
10101

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✨ Key Takeaway (Patterns + Conditions)

• j < n → full row (square)

• j <= i → grows with row (triangle)

• j < n-i → shrinks with row (inverted)

• toggle → switches between 0/1