Implementing Array Algorithms

Standard array algorithms

• Most array tasks are a traversal 遍历 plus one of a few standard patterns.
• Sum / average: accumulate a total, then divide by length.
• Count: increment when an element matches a condition.
• Min / max: track the smallest or largest seen so far.

Finding the maximum

• Start max = a[0] (the first element), then traverse from index 1.
• if (a[i] > max) { max = a[i]; } inside the loop.
• After the loop, max holds the largest value in the array.
• Start from the first element, not 0 — 0 could be larger than every value.

Finding the maximum of an array, traced pass by pass

Searching for a value

• To check if a value is present, traverse and compare each element.
• Return the index 下标 where it's found, or -1 if the loop finishes without a match.
• if (a[i] == target) return i; inside the loop; return -1; after.
• This is a linear search 线性查找 (Unit 4.14 covers it in depth).

Shifting and modifying

• Some algorithms move or change elements — e.g. shift everything left, or double each value.
• Modifying needs the indexed loop so you can assign a[i] = ....
• Watch bounds when reading a[i+1] — the last index has no neighbor.
• Trace the indices carefully to avoid an out-of-bounds access.