DSA · Theory

Sort an Array of 0's, 1's, and 2's

Theory

179/810

Sort an Array of 0's, 1's, and 2's is simple if you keep it on paper. Amit uses it for names A→Z in the roll list.

Sort an Array of 0's, 1's, and 2's order: meaning → n log n vs n² → one limit. Dumping ten features helps nobody.

Skip Sort an Array of 0's, 1's, and 2's and unstable sort when equal keys matter shows up in the roll list.

Amit ships Sort an Array of 0's, 1's, and 2's in the roll list. That is the use case worth saying.

Don’t do this with Sort an Array of 0's, 1's, and 2's: unstable sort when equal keys matter. Interviewers spot it in ten seconds.

After Sort an Array of 0's, 1's, and 2's, Amit should still remember unstable sort when equal keys matter.

Viva for Sort an Array of 0's, 1's, and 2's: what it is → n log n vs n² → the mistake (unstable sort when equal keys matter).

Diagram

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

Exam tip

Say Sort an Array of 0's, 1's, and 2's in one breath, then n log n vs n², then unstable sort when equal keys matter.

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

Sort an Array of 0's, 1's, and 2's — arrays give O(1) index access; matrices are arrays of arrays.

DefSort an Array of 0's, 1's, and 2's — Amit uses it for names A→Z in the roll list.
RuleSort an Array of 0's, 1's, and 2's → n log n vs n².
RememberSort an Array of 0's, 1's, and 2's + time vs memory (the roll list).
UseSort an Array of 0's, 1's, and 2's in the roll list (names A→Z).
TrapSort an Array of 0's, 1's, and 2's — unstable sort when equal keys matter.
ExSort an Array of 0's, 1's, and 2's → names A→Z.