724. Find Pivot Index

// LeetCode URL: https://leetcode.com/problems/find-pivot-index/
/**
 * Prefix Sum
 *
 * leftSum = rightSum (Excluding the pivot point)
 *
 * rightSum = TotalSum - leftSum - nums[pivotPoint]
 *
 * Time Complexity: O(N)
 *
 * Space Complexity: O(1)
 *
 * N = Length of the input nums array.
 */
class Solution {
    public int pivotIndex(int[] nums) {
        if (nums == null || nums.length == 0) {
            return -1;
        }

        int sum = 0;
        int leftSum = 0;
        for (int num : nums) {
            sum += num;
        }

        for (int i = 0; i < nums.length; i++) {
            if (leftSum == sum - leftSum - nums[i]) {
                return i;
            }
            leftSum += nums[i];
        }

        return -1;
    }
}