message: Update find-all-duplicates-in-an-array.cpp
diff: // Space: O(1)
  class Solution {
  +public:
  + vector<int> findDuplicates(vector<int>& nums) {
  + vector<int> result;
  + for (const auto& i : nums) {
  + if (nums[abs(i) - 1] < 0) {
  + result.emplace_back(abs(i));
  + } else {
  + nums[abs(i) - 1] *= -1;
  + }
  + }
  + return result;
  + }
  +};
  +
  +class Solution2 {
  public:
  vector<int> findDuplicates(vector<int>& nums) {
  vector<int> result;
  