P03 — Accumulation — every solution explained

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What is inside

• 1. Sum of elements at even indices
• 2. Sum of even-VALUED elements. (Not the same as 1 -- read carefully.)
• 3. Running maximum after each step
• 4. Count elements strictly greater than the running average so far
• 5. Longest run of equal consecutive values
• 6. Alternating sum: a0 - a1 + a2 -
• 7. Count how many prefix sums are divisible by k
• 8. Index of the first element greater than a threshold, else -1
• 9. Sum, applying +10% to every third element (index 2, 5, 8...). Integer arithmetic, truncating -- states the rounding rule explicitly
• 10. Count sign changes between consecutive elements (zeros are skipped)
• 11. Maximum sum of any contiguous subarray (Kadane). Allows all-negative
• 12. Total of values that are divisible by d, minus (index % m)