When should I use prefix & suffix?

Use it when: Many range sum / product / min queries. You need "everything except index i" in linear time. Stateless transforms on immutable arrays.

What are the most common prefix & suffix bugs?

Off-by-one between prefix length n+1 and array length n. Using integer types that overflow for products (switch to explicit big-int if needed). Recomputing prefixes inside the query loop — defeats the whole pattern.

What problems use the prefix & suffix pattern?

Representative scenarios: Exclusive Revenue — product of array except self. Range Tally — sum over [l, r]. Running Balance — detect first index where total flips sign.

Is prefix & suffix on the Blind 75?

Yes — Prefix & Suffix is one of the core patterns behind the Blind 75 list. See /blind-75 for the complete mapping.

Pattern · Preprocess O(n); query O(1).

Prefix & Suffix — the shape behind dozens of interview problems.

TL;DR

Precompute cumulative arrays so range queries answer in O(1). Preprocess O(n); query O(1).

When to reach for Prefix & Suffix

Many range sum / product / min queries.
You need "everything except index i" in linear time.
Stateless transforms on immutable arrays.

Scenario variants (legal, original)

Exclusive Revenue — product of array except self.
Range Tally — sum over [l, r].
Running Balance — detect first index where total flips sign.

Prefix & Suffix in Python

def range_sum(nums: list[int]) -> list[int]:
    pre = [0]
    for v in nums:
        pre.append(pre[-1] + v)
    return pre  # pre[r+1] - pre[l] gives sum of nums[l..r]

See language-specific tabs at /languages/python/patterns and the SQL variant at /languages/sql/patterns.

Common bugs

Off-by-one between prefix length n+1 and array length n.
Using integer types that overflow for products (switch to explicit big-int if needed).
Recomputing prefixes inside the query loop — defeats the whole pattern.

Related patterns

Sliding Window Two Pointers Binary Search on Answer Back to all 12

Frequently asked questions

What is the prefix & suffix pattern?: Prefix & Suffix is precompute cumulative arrays so range queries answer in o(1). Preprocess O(n); query O(1).
When should I use prefix & suffix?: Use it when: Many range sum / product / min queries. You need "everything except index i" in linear time. Stateless transforms on immutable arrays.
What are the most common prefix & suffix bugs?: Off-by-one between prefix length n+1 and array length n. Using integer types that overflow for products (switch to explicit big-int if needed). Recomputing prefixes inside the query loop — defeats the whole pattern.
What problems use the prefix & suffix pattern?: Representative scenarios: Exclusive Revenue — product of array except self. Range Tally — sum over [l, r]. Running Balance — detect first index where total flips sign.
Is prefix & suffix on the Blind 75?: Yes — Prefix & Suffix is one of the core patterns behind the Blind 75 list. See /blind-75 for the complete mapping.

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