README.md

2485. Find the Pivot Integer

Given a positive integer n, find the pivot integer x such that:

• The sum of all elements between 1 and x inclusively equals the sum of all elements between x and n inclusively.

Return the pivot integer x. If no such integer exists, return -1. It is guaranteed that there will be at most one pivot index for the given input.

Example 1:

Input: n = 8
Output: 6
Explanation: 6 is the pivot integer since: 1 + 2 + 3 + 4 + 5 + 6 = 6 + 7 + 8 = 21.

Example 2:

Input: n = 1
Output: 1
Explanation: 1 is the pivot integer since: 1 = 1.

Example 3:

Input: n = 4
Output: -1
Explanation: It can be proved that no such integer exist.

Constraints:

• 1 <= n <= 1000

Solutions (Rust)

1. Solution

impl Solution {
    pub fn pivot_integer(n: i32) -> i32 {
        let x = ((n * (n + 1) / 2) as f64).sqrt() as i32;

        if x * x * 2 == n * (n + 1) {
            x
        } else {
            -1
        }
    }
}