Sort an array of 0s, 1s and 2s | Dutch National Flag problem

Sort an array of 0s, 1s and 2s (dutch national flag problem) is a DSA topic. In plain words you use it for names A→Z in the roll list. Don’t start with a slogan — start with that picture.

Smallest example: n log n vs n². Type it, run it, and say what you see. If you can do that from memory, you know Sort an array of 0s, 1s and 2s (dutch national flag problem).

From the example next to this theory: Sort an array of 0s, 1s and 2s | Dutch National Flag problem — arrays give O(1) index access; matrices are arrays of arrays.

Trap — unstable sort when equal keys matter. Fix that before you talk about advanced DSA.

Viva: what is Sort an array of 0s, 1s and 2s (dutch national flag problem)? Then show n log n vs n². Then name the trap.

Diagram

  index →  0    1    2
  array → [10,  20,  30]

Exam tip

What is Sort an array of 0s, 1s and 2s (dutch national flag problem)? Show this: n log n vs n². Trap: unstable sort when equal keys matter.

Example

arr = [10, 20, 30, 40]
print(arr[2], arr[-1])
matrix = [[1, 2], [3, 4]]
print(matrix[1][0])  # 3

Sort an array of 0s, 1s and 2s | Dutch National Flag problem — arrays give O(1) index access; matrices are arrays of arrays.

Short notes

DefSort an array of 0s, 1s and 2s (dutch national flag problem) — names A→Z in the roll list.
Rulen log n vs n²
Trapunstable sort when equal keys matter
Usethe roll list

Sort an array of 0s, 1s and 2s | Dutch National Flag problem

Sort an array of 0s, 1s and 2s (dutch national flag problem) is a DSA topic. In plain words you use it for names A→Z in the roll list. Don’t start with a slogan — start with that picture.

Smallest example: n log n vs n². Type it, run it, and say what you see. If you can do that from memory, you know Sort an array of 0s, 1s and 2s (dutch national flag problem).

From the example next to this theory: Sort an array of 0s, 1s and 2s | Dutch National Flag problem — arrays give O(1) index access; matrices are arrays of arrays.

Trap — unstable sort when equal keys matter. Fix that before you talk about advanced DSA.

Viva: what is Sort an array of 0s, 1s and 2s (dutch national flag problem)? Then show n log n vs n². Then name the trap.

Diagram

  index →  0    1    2
  array → [10,  20,  30]

Exam tip

What is Sort an array of 0s, 1s and 2s (dutch national flag problem)? Show this: n log n vs n². Trap: unstable sort when equal keys matter.

Example

arr = [10, 20, 30, 40]
print(arr[2], arr[-1])
matrix = [[1, 2], [3, 4]]
print(matrix[1][0])  # 3

Sort an array of 0s, 1s and 2s | Dutch National Flag problem — arrays give O(1) index access; matrices are arrays of arrays.

Short notes

DefSort an array of 0s, 1s and 2s (dutch national flag problem) — names A→Z in the roll list.
Rulen log n vs n²
Trapunstable sort when equal keys matter
Usethe roll list

Sort an array of 0s, 1s and 2s | Dutch National Flag problem

Example

Short notes

Questions

Sort an array of 0s, 1s and 2s | Dutch National Flag problem

Example

Short notes

Questions