Given an array A[] and a number x, check for pair in A[] with sum as x (aka Two Sum)

Given an array A[] and a number x, check for pair in A[] with sum as x (aka Two Sum) is a DSA topic. In plain words you use it for a short Given an array A[] and a number x, check for pair in A[] with sum as x aka Two Sum example in a short dry-run on paper. Don’t start with a slogan — start with that picture.

Smallest example: the smallest Given an array A[] and a number x, check for pair in A[] with sum as x aka Two Sum example you can type. Type it, run it, and say what you see. If you can do that from memory, you know Given an array A[] and a number x, check for pair in A[] with sum as x (aka Two Sum).

From the example next to this theory: Given an array A[] and a number x, check for pair in A[] with sum as x (aka Two Sum) — arrays give O(1) index access; matrices are arrays of arrays.

Trap: only saying “Given an array A[] and a number x, check for pair in A[] with sum as x aka Two Sum” with no example. Fix that before you talk about advanced DSA.

Viva: what is Given an array A[] and a number x, check for pair in A[] with sum as x (aka Two Sum)? Then show the smallest Given an array A[] and a number x, check for pair in A[] with sum as x aka Two Sum example you can type. Then name the trap.

Diagram

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

Exam tip

What is Given an array A[] and a number x, check for pair in A[] with sum as x (aka Two Sum)? Show this: the smallest Given an array A[] and a number x, check for pair in A[] with sum as x aka Two Sum example you can type. Trap: only saying “Given an array A[] and a number x, check for pair in A[] with sum as x aka Two Sum” with no example.

Example

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

Given an array A[] and a number x, check for pair in A[] with sum as x (aka Two Sum) — arrays give O(1) index access; matrices are arrays of arrays.

Short notes

DefGiven an array A[] and a number x, check for pair in A[] with sum as x (aka Two Sum) — a short Given an array A[] and a number x, check for pair in A[] with sum as x aka Two Sum example in a short dry-run on paper.
Rulethe smallest Given an array A[] and a number x, check for pair in A[] with sum as x aka Two Sum example you can type
Traponly saying “Given an array A[] and a number x, check for pair in A[] with sum as x aka Two Sum” with no example
Usea short dry-run on paper

Given an array A[] and a number x, check for pair in A[] with sum as x (aka Two Sum)

From the example next to this theory: Given an array A[] and a number x, check for pair in A[] with sum as x (aka Two Sum) — arrays give O(1) index access; matrices are arrays of arrays.

Trap: only saying “Given an array A[] and a number x, check for pair in A[] with sum as x aka Two Sum” with no example. Fix that before you talk about advanced DSA.

Diagram

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

Exam tip

Given an array A[] and a number x, check for pair in A[] with sum as x (aka Two Sum)

Example

Short notes

Questions

Given an array A[] and a number x, check for pair in A[] with sum as x (aka Two Sum)

Example

Short notes

Questions