Common Signals Between Space Probes II

Unit 2 Session 1 (Click for link to problem statements)

U-nderstand

Understand what the interviewer is asking for by using test cases and questions about the problem.

• Q: What is the problem asking for?

  • A: The problem asks to calculate two values:
    • answer1: the number of indices i such that signals1[i] exists in signals2.
    • answer2: the number of indices j such that signals2[j] exists in signals1.

• Q: What are the inputs?

  • A: Two integer arrays signals1 and signals2 of sizes n and m, respectively.

• Q: What are the outputs?

  • A: A list [answer1, answer2] where:
    • answer1 is the count of elements in signals1 that exist in signals2.
    • answer2 is the count of elements in signals2 that exist in signals1.

• Q: Are there any constraints on the values in the arrays?

  • A: The values are integers, and the arrays can be of different lengths.

P-lan

Plan the solution with appropriate visualizations and pseudocode.

Note: Like many interview questions, this problem can be solved in many ways. If you chose to approach this using dictionaries, check out the Common-Signals-Between-Space-Probes solution guide.

General Idea: Use sets to find common elements between the two arrays and count occurrences.

1. Convert `signals1` and `signals2` to sets `set_signals1` and `set_signals2`.
2. Initialize `answer1` to 0 to count elements in `signals1` that are in `signals2`.
3. Initialize `answer2` to 0 to count elements in `signals2` that are in `signals1`.
4. Iterate through `signals1` and increment `answer1` for each element found in `set_signals2`.
5. Iterate through `signals2` and increment `answer2` for each element found in `set_signals1`.
6. Return the list `[answer1, answer2]`.

I-mplement

def find_common_signals(signals1, signals2):
    # Convert signals to a set
    set_signals1 = set(signals1)
    set_signals2 = set(signals2)

    # Calculate answer1: the number of indices i such that signals1[i] exists in signals2
    answer1 = 0
    for signal in signals1:
        if signal in set_signals2:
            answer1 += 1

    # Calculate answer2: the number of indices j such that signals2[j] exists in signals1
    answer2 = 0
    for signal in signals2:
        if signal in set_signals1:
            answer2 += 1

    return [answer1, answer2]