First Match: Trace Before You Choose

Find the first value that meets a rule, and distinguish its value from its position and the number of checks.

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Keep the supplied order. Start result at 0. Test each value against value >= 2. At the first match, copy the value and stop this scan. Continue with the report after the loop. If nothing matches, keep fallback 0; it is not a found item. Item numbers on this page begin at 1.

Worked example

For [0, 4, 3], inspect 0 (false), then 4 (true). Copy 4 at item 2 and stop. Two comparisons ran. The later 3 was not inspected.

Four positions labeled item 1 through item 4 contain 1, 0, 3 and 4. Their comparison results are left for the learner. — Trace only the comparisons that actually run.

Would you believe it?

The lists [3, 2] and [2, 3] have the same values, length and sum. Yet searching in order for the first value at least 2 selects 3 from the first list and 2 from the second. Order can change the answer.

Python: ordered iteration and loop control

The next delivery list

Use [1, 0, 3, 4] in that exact order. The rule is value >= 2, the starting result is 0, and the report comes after the loop. Do not sort, add all matches, or keep searching after copying the first match.

Question 1 Which result is copied from [1, 0, 3, 4]? 4, because it is the largest 3, the first value at least 2 2, because it is the threshold

Question 2 How many comparisons run for this list? 3 4 2

Question 3 Which value is not inspected? 0 3 4

Question 4 For a separate list [2, 4], which result and number of comparisons are correct? 4 after two comparisons 2 after one comparison 0 after no comparisons

Question 5 For a separate list [1, 0], what does result 0 mean? No match; the stated fallback remains The zero at item 2 matched The report after the loop never runs

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