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partition

//全部被 pred 判定为 true 的元素，都被放到前段
//被 pred 判定为 false 的元素，都被放到后段
//不保证保留相对位置
template <class BidirectionalIterator, class Predicate>
BidirectionalIterator partition(BidirectionalIterator first,
                                BidirectionalIterator last, Predicate pred) {
  while (true) {
    while (true)
      if (first == last)
        return first;
      else if (pred(*first))
        ++first;
      else
        break;
    --last;
    while (true)
      if (first == last)
        return first;
      else if (!pred(*last))
        --last;
      else
        break;
    iter_swap(first, last);
    ++first;
  }
}

int A[] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
const int N = sizeof(A)/sizeof(int);
partition(A, A + N,
          compose1(bind2nd(equal_to<int>(), 0),
                   bind2nd(modulus<int>(), 2)));
copy(A, A + N, ostream_iterator<int>(cout, " "));
// The output is "10 2 8 4 6 5 7 3 9 1".