Count Complete Rows in a Coin Staircase
Company: Meta
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: easy
Interview Round: Other
# Count Complete Rows in a Coin Staircase
Build rows of coins in order, using exactly `i` coins in row `i`, beginning with row one. Given `n` coins, return the number of complete rows you can build. Any coins left for an incomplete next row do not count as another complete row.
### Function
`int arrangeCoins(int n)`
### Example 1
```text
Input: n = 10
Output: 4
```
Four complete rows use `1+2+3+4=10` coins.
### Example 2
```text
Input: n = 2
Output: 1
```
The first row is complete, but only one coin remains for the two-coin second row.
### Constraints
- `1 <= n <= 2147483647`.
### Clarifications
Rows must use `1,2,3,...` coins without skipping a row. Return the number completed, not the number of coins left or the partially started final row.
### What a Strong Answer Covers
- Exact triangular totals and an incomplete next row.
- The full signed 32-bit input range.
- Why the returned row count is feasible and the next count is not.
- Arithmetic safety and resource bounds.
Overview: Practice counting complete staircase rows from a coin total. Handle exact triangular totals, partial final rows, and overflow-safe arithmetic across the full input range.