Grokking #232

class TimeMap {

    // key -> map of timestamp, value
    Map<String, NavigableMap<Integer, String>> segments;

    public TimeMap() {
        segments = new HashMap<>();
    }

    public void set(String key, String value, int timestamp) {
        NavigableMap<Integer, String> timeMap =
            segments.computeIfAbsent(key, k -> new TreeMap<>());
        timeMap.put(timestamp, value);
    }

    public String get(String key, int timestamp) {
        return Optional.ofNullable(segments.get(key))
            .flatMap(timeMap ->
                    Optional.ofNullable(timeMap.floorEntry(timestamp)))
            .map(entry -> entry.getValue())
            .orElse("");
    }
}