Method erase

code/data-structures/misof_tree.cpp:7–8

  void insert(int x) {
    for (int i = 0; i < BITS; cnt[i++][x]++, x >>= 1); }
  void erase(int x) {
    for (int i = 0; i < BITS; cnt[i++][x]--, x >>= 1); }
  int nth(int n) {
    int res = 0;
    for (int i = BITS-1; i >= 0; i--)