findBalancePoint.js

function findBalancePoint(array) {
  if (array.length === 0) {
    return 0;
  }
  if (array.length === 1) {
    return 1;
  }
  // initial sums
  var left = 0;
  var right = 0;
  
  // squeeze array
  for (var i = 0, j = array.length - 1; i < j;) {
    if (left < right) {
      left += array[i++];
    } else if (left > right) {
      right += array[j--];
    } else {
      left += array[i++];
      right += array[j--];
    }
  }
  return left === right ? 1 : 0;
}

function test(array, expected) {
  var result = findBalancePoint(array);
  console.log(result === expected ? 'ok:' : 'failed:', array);
}

test([-1, 4, 3, 3], 1);
test([1, 2, 3, 3], 1);
test([], 0);
test([1], 1);
test([1, 2], 0);
test([2, 2], 1);
test([2, 4, 4, 2], 1);
test([0, 0, 0, 1, 1, 1], 1);
test([0, 0, 0, 1, 1, 5], 0);