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## What It Does

This function counts the number of **unique elements** in a sorted array. The `index` pointer tracks the start of the current group of duplicate values, while `cursor` scans forward. When a new distinct value is found, `ans` increments and `index` jumps to `cursor`. The `+ 1` at the end accounts for the final group, which never triggers a mismatch to count itself.

For example, `[1, 1, 2, 3, 3, 3, 4]` → returns `4`.

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## Complexity Analysis

**Time Complexity: O(n)**

`cursor` advances by 1 on every iteration and never backtracks, so the loop runs exactly `n` times — a single linear pass through the array.

**Space Complexity: O(1)**

Only three integer variables (`cursor`, `ans`, `index`) are used regardless of input size. No additional data structures are allocated.

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## A Few Notes

**It assumes a sorted array.** The duplicate-detection logic only works because identical values are guaranteed to be adjacent. On an unsorted array it would produce incorrect results.

**The variable naming could be clearer.** `index` and `cursor` are both just integer indices, making the code a bit harder to read at a glance. Something like `left`/`right` or `groupStart`/`scanner` would better convey their roles.

**`ans` is slightly misleading** since it's an intermediate count, not the final answer — it holds `uniqueCount - 1` until the return statement corrects it.

First solved

Mar 2, 2026