724.js

/** ------------------------------------------------------------------------------
 * 
 * 724. Find Pivot Index
 * Topics: prefix Sum
 * https://leetcode.com/problems/find-pivot-index/
 * 
 ------------------------------------------------------------------------------ */
/**
 * @param {number[]} nums
 * @return {number}
 */
var pivotIndex = function (nums) {
  const sum = nums.reduce((acc, cur) => acc + cur, 0)

  let left = 0

  for (let i = 0; i < nums.length; i++) {
    const right = sum - left - nums[i]
    if (left === right) return i
    left += nums[i]
  }
  return -1
}

console.log(pivotIndex([-1, -1, -1, -1, -1, -1]))