Programming Readiness: Lists/Arrays and Traversal

This module supports R3 and R6. All work here is formative. Pick Java or Python and stay with it.

Specification checklist

Traced/worked example

Target-sum with nested loops:

for (int i = 0; i < nums.length; i++) {
    for (int j = i + 1; j < nums.length; j++) {
        if (nums[i] + nums[j] == target) return true;
    }
}
return false;

For {2, 3, 5, 9, 12} and target 5, i = 0, j = 1 finds 2 + 3 and returns true. For {3} and target 6, j never runs, so the answer is false. If the inner loop started at i, 3 + 3 would incorrectly count as a pair.

Practice

Guided: List every (i, j) pair for {2, 0, 5, 6, 4} with j = i + 1. Does any pair add to 12?

Independent: Implement nested-loop targetSumNested and countDistinctNested.

Java: Practice.java, PracticeTest.java

javac Practice.java PracticeTest.java && java PracticeTest

Python: practice.py

python3 practice.py

Common mistakes

• Reusing the same index for both addends.
• Starting the distinct inner loop at 0 through length instead of only earlier indexes.
• Returning true for an empty list.

Exit guidance

Complete the self-check and tests. Explain why {3, 3} and target 6 is true while {3} is false.

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