Chain Reorg Balances

A wallet indexer receives blocks in arrival order. Each element of blocks is [height, transfers], where transfers is a list of [account, amount] balance changes (amounts may be negative).

The chain starts empty, so the first block has height 1. Let tip be the height of the current last block. Each arriving block has 1 <= height <= tip + 1:

• If height == tip + 1, the block extends the chain.
• If height <= tip, a reorg happened: every block currently at height height or above is discarded and its transfers are undone, and then the new block is added at height (it becomes the new tip).

A balance is the sum of the transfer amounts for that account across the blocks currently on the chain. Return [account, balance] for every account whose final balance is nonzero, sorted by account name.