sclass LCSortedPairIndex {
  long[] pairs;
  int[] index;
  
  *(long[] pairs) {
    this(pairs, null);
  }
  
  *(long[] *pairs, LCSortedPairIndex primer) {
    index = lc_sortedPairIndex(pairs, primer?.index);
  }
  
  int get(long pair) {
    int i = intArrayBinarySearchWithGeneralizedComparator(index,
      a -> cmp(pairs[a], pair));
    ret i >= 0 ? i : -1;
  }
}