DSA · Theory

Substring Check

Theory

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Substring Check is simple if you keep it on paper. Priya uses it for folder on disk in a file explorer.

For Substring Check, a dry-run table is in play. Don’t blame it until you have traced folder on disk.

Substring Check exists so Priya can keep folder on disk correct in a file explorer.

Use Substring Check when folder on disk must stay clear. If a simpler DSA step works, use that instead.

Substring Check trap — unbalanced BST becoming a list. Priya loses marks for that every viva.

After Substring Check, Priya should still remember unbalanced BST becoming a list.

Viva for Substring Check — what it is → left < root < right → the mistake (unbalanced BST becoming a list).

Diagram

Exam tip

Say Substring Check in one breath, then left < root < right, then unbalanced BST becoming a list.

# Substring Check
data = [4, 1, 3]
print("start", data)
if data[0] > data[1]:
    data[0], data[1] = data[1], data[0]
print("after one step", data)

Substring Check: dry-run [4, 1, 3]. Say the list after one step.