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#2485 - Find the Pivot Integer
Problem Description
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.
Solution
/**
* @param {number} n
* @return {number}
*/
var pivotInteger = function(n) {
const totalSum = n * (n + 1) / 2;
const pivot = Math.sqrt(totalSum);
return Number.isInteger(pivot) && pivot <= n ? pivot : -1;
};