Map<String, String> memoized;

String SegmentString(String input, Set<String> dict) {
if (dict.contains(input)) return input;
if (memoized.containsKey(input) {
return memoized.get(input);
}
int len = input.length();
for (int i = 1; i < len; i++) {
String prefix = input.substring(0, i);
if (dict.contains(prefix)) {
String suffix = input.substring(i, len);
String segSuffix = SegmentString(suffix, dict);
if (segSuffix != null) {
memoized.put(input, prefix + " " + segSuffix);
return prefix + " " + segSuffix;

}
}
memoized.put(input, null);
return null;
}

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