Equilibrium index

index.js

"use strict";

//An equilibrium index of a sequence is an index into the sequence such that the sum of elements at lower indices is equal to the sum of elements at higher indices.

//two loops
function eq(arr) {
  if (arr.length === 0) {
    return -1;
  }
  for (var i = 0; i < arr.length; i++) {
    var lsum = 0;
    var rsum = 0;
    for (var j = 0; j < arr.length; j++) {
      if (j < i) {
        lsum += arr[j];
      } else if (j > i) {
        rsum += arr[j];
      }
    }
    if (lsum === rsum) {
      return i;
    }
  };
  return -1;
}

//three loops
function eq2(arr) {
  if (arr.length === 0) {
    return -1;
  }
  for (var i = 0; i < arr.length; i++) {
    var lsum, rsum;
    lsum = rsum = 0;
    for (var j = 0; j < i; j++) {
      lsum += arr[j];
    }
    for (var k = i + 1; k < arr.length; k++) {
      rsum += arr[k];
    }
    if (lsum === rsum) {
      return i;
    }
  }
  return -1;
}