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LeetCode

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Problem

You have n coins and you want to build a staircase with these coins. The staircase consists of k rows where the ith row has exactly i coins. The last row of the staircase may be incomplete.

Given the integer n, return the number of complete rows of the staircase you will build.

Example 1:

img

Input: n = 5
Output: 2
Explanation: Because the 3rd row is incomplete, we return 2.

Example 2:

img

Input: n = 8
Output: 3
Explanation: Because the 4th row is incomplete, we return 3.

Code

class Solution {
    public int arrangeCoins(int n) {
        return (int)(Math.sqrt(2 * (long)n + 0.25) - 0.5);
    }
}