DSA interview question

Replace Elements by Their Rank

Easy · Data structures · Topics: heap, sorting, hash map

The problem

A contest dashboard wants to show each score's rank instead of the raw number: the smallest score gets rank 1, the next distinct score rank 2, and so on, with equal scores sharing a rank. Process the values in increasing order with a min-heap of (value, index) pairs. Each time the popped value differs from the previous one, the rank goes up by one, and the rank is written back to that element's original index.

Example: [20, 15, 26, 2, 98, 6] → [4, 3, 5, 1, 6, 2].

Function signature

vector<int> replaceWithRank(const vector<int>& arr);

Test cases

Input	Output	Explanation
`[20, 15, 26, 2, 98, 6]`	`[4, 3, 5, 1, 6, 2]`	Sorted: 2, 6, 15, 20, 26, 98
`[2, 2, 1, 6]`	`[2, 2, 1, 3]`	Equal values share a rank
`[-5, 10, -5, 0]`	`[1, 3, 1, 2]`
`[1, 1, 1]`	`[1, 1, 1]`
`[5]`	`[1]`

(Confirm: ranks are dense (no gaps after ties) and start at 1.)

How interviewers phrase it

"Replace each element of the array by its rank; the smallest element gets rank 1 and equal elements share a rank" (GeeksforGeeks "Replace elements by its rank in the array"; LeetCode 1331 "Rank Transform of an Array").

Clarifying questions to ask

Dense ranks (1, 1, 2) or competition ranks (1, 1, 3)? (Dense.)
Do equal values share a rank? (Yes.)
Can values be negative? (Yes.)

Follow-ups to expect

"Why use a heap?"
"Sorting alternative?"
"How do ties work?"
"What's this used for?"
"Complexity?"

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