Candlestick Chart

Build a simplified candlestick chart generator that aggregates a stream of price updates into fixed 10-unit time intervals. Each interval (bucket) must report the open, close, high, and low prices that occurred within it. The input is a comma-separated string of price:timestamp pairs sorted by timestamp (e.g. “1:0,3:10,2:12,4:19,5:35”). The timestamp is treated as the bucket key: bucket = (timestamp // 10) * 10. For every bucket that contains at least one price you must emit a candle in the exact string format “{start,first,last,max,min}”. If a bucket has no prices but earlier buckets exist, synthesize a candle by copying the previous bucket’s close price into all four fields (open, close, high, low). If there is no previous bucket, skip the empty bucket. Buckets must be emitted in ascending start-time order with no gaps in the output sequence; any missing bucket keys between the earliest and latest observed buckets must be filled with the carry-forward rule above. Return the concatenated candle strings with no separators.