message: Update maximum-number-of-pairs-in-array.cpp
diff: class Solution {
  public:
  vector<int> numberOfPairs(vector<int>& nums) {
  - static const int MAX_NUM = 100;
  - vector<int> cnt(MAX_NUM + 1);
  + vector<int> cnt(*max_element(cbegin(nums), cend(nums)) + 1);
  int pair_cnt = 0;
  for (const auto& x : nums) {
  cnt[x] ^= 1;
  