function balancedSums(arr: number[]): string {
  if (arr.length === 1) {
    return 'YES';
  }
  
  let balanceIdx = Math.floor(arr.length/2);
  let leftSum = arr.slice(0, balanceIdx).reduce((total, val) => total + val, 0);
  let rightSum = arr.slice(balanceIdx+1).reduce((total, val) => total + val, 0);
  
  if (leftSum === rightSum) {
    return 'YES';
  }
  
  const dir = leftSum < rightSum ? 1 : -1;
  
  while (balanceIdx !== -1 && balanceIdx !== arr.length) {
    const prevBalancePt = arr[balanceIdx];
    balanceIdx += dir;
    const newBalancePt = arr[balanceIdx];
    
    if (dir === 1) {
      leftSum += prevBalancePt;
      rightSum -= newBalancePt;
    } else {
      leftSum -= prevBalancePt;
      rightSum += newBalancePt;
    }
    
    if (leftSum === rightSum) {
     return 'YES';
    }
  }
  
  return 'NO';
}