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DSA · Theory

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

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Theory

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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 simple if you keep it on paper. Priya uses it for Given an array A[] and a number x, check for pair in A[] with sum as x aka Two Sum on Priya's board in a viva board.

For Given an array A[] and a number x, check for pair in A[] with sum as x (aka Two Sum), a dry-run table is in play. Don’t blame it until you have traced Given an array A[] and a number x, check for pair in A[] with sum as x aka Two Sum on Priya's board.

Given an array A[] and a number x, check for pair in A[] with sum as x (aka Two Sum) exists so Priya can keep Given an array A[] and a number x, check for pair in A[] with sum as x aka Two Sum on Priya's board correct in a viva board.

Given an array A[] and a number x, check for pair in A[] with sum as x (aka Two Sum) shows up in a viva board. Name Given an array A[] and a number x, check for pair in A[] with sum as x aka Two Sum on Priya's board, not “a real-world scenario”.

If Given an array A[] and a number x, check for pair in A[] with sum as x aka Two Sum on Priya's board breaks under Given an array A[] and a number x, check for pair in A[] with sum as x (aka Two Sum), check copy-pasting Given an array A[] and a number x, check for pair in A[] with sum as x aka Two Sum without a dry-run first.

After Given an array A[] and a number x, check for pair in A[] with sum as x (aka Two Sum), Priya should still remember copy-pasting Given an array A[] and a number x, check for pair in A[] with sum as x aka Two Sum without a dry-run.

Close Given an array A[] and a number x, check for pair in A[] with sum as x (aka Two Sum) with: “If I skip it, Given an array A[] and a number x, check for pair in A[] with sum as x aka Two Sum on Priya's board goes wrong like this: copy-pasting Given an array A[] and a number x, check for pair in A[] with sum as x aka Two Sum without a dry-run.”

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

Say Given an array A[] and a number x, check for pair in A[] with sum as x (aka Two Sum) in one breath, then one Given an array A[] and a number x, check for pair in A[] with sum as x aka Two Sum step Priya can write from memory, then copy-pasting Given an array A[] and a number x, check for pair in A[] with sum as x aka Two Sum without a dry-run.

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) — Priya uses it for Given an array A[] and a number x, check for pair in A[] with sum as x aka Two Sum on Priya's board in a viva board.
  • RuleGiven an array A[] and a number x, check for pair in A[] with sum as x (aka Two Sum) → one Given an array A[] and a number x, check for pair in A[] with sum as x aka Two Sum step Priya can write from memory.
  • RememberGiven an array A[] and a number x, check for pair in A[] with sum as x (aka Two Sum) + a dry-run table (a viva board).
  • UseGiven an array A[] and a number x, check for pair in A[] with sum as x (aka Two Sum) in a viva board (Given an array A[] and a number x, check for pair in A[] with sum as x aka Two Sum on Priya's board).
  • TrapGiven an array A[] and a number x, check for pair in A[] with sum as x (aka Two Sum) — copy-pasting Given an array A[] and a number x, check for pair in A[] with sum as x aka Two Sum without a dry-run.
  • ExGiven 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 on Priya's board.

Questions

1

Priya asks: why does Given an array A[] and a number x, check for pair in A[] with sum as x (aka Two Sum) exist? Use Given an array A[] and a number x, check for pair in A[] with sum as x aka Two Sum on Priya's board.

2

If you skip Given an array A[] and a number x, check for pair in A[] with sum as x (aka Two Sum), what breaks in a viva board?

3

Which mistake makes Given an array A[] and a number x, check for pair in A[] with sum as x aka Two Sum on Priya's board fail?

4

Write the smallest Given an array A[] and a number x, check for pair in A[] with sum as x (aka Two Sum) step on Given an array A[] and a number x, check for pair in A[] with sum as x aka Two Sum on Priya's board. What happens?

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