FindThePivotInteger.java

/*
problem link: https://leetcode.com/problems/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*/

public class FindThePivotInteger {
    public int pivotInteger(int n) {
        if (n == 1) {
            return n;
        }
        int sum = 1;
        for (int i = 2; i < n; i++) {
            sum += i;
            if (sum == sumToN(i, n)) {
                return i;
            }
        }
        return -1;

    }

    public int sumToN(int i, int n) {
        int sum = 0;
        for (int value = i; value <= n; value++) {
            sum += value;
        }
        return sum;
    }
}