How to detect duplicates in a vector of unordered_map?

Given a vector of unordered_map<u_int,int>, I would like to check if the vector contains any duplicated values. I know the comparison operator exists for unordered_maps, but I would like to avoid the pairwise comparison of each element with each other. One classical solution is to insert the values of the vector into a set, then to compare the number of elements in the set and the vector. However, the problem here is that the object to be inserted into the set must have the comparison operators overloaded. In case of the unordered_set, the hash function to be used must be overloaded for the complex object. In order to overload, I need to derive a class from the std::unordered_map. Then I need to overload either the comparison operator or the hash function. Another solution that I could think of is to concatenate all of the key value pairs into a string, then sort the string by the keys and detect the duplicates on those strings. I wonder what would be the best solution for this problem.
Example data:

using namespace std;
typedef unordered_map<u_int,int> int_map;
int_map a = { {1,1}, {2,4}, {3,5} };
int_map b = { {1,1}, {2,-1}, {4,-2} };
int_map c = { {1,1}, {3,5} };

vector<unordered_map<u_int,int>> my_vec;

my_vec.push_back(a);
my_vec.push_back(b);
my_vec.push_back(c);

The contents of my_vec is:
{ { 1 => 1, 2 => 4, 3 => 5 },
{ 1 => 1, 2 => -1, 4 => -2 },
{ 1 => 1, 3 => 5 } }

Please feel free to ask/commend/edit if the question is not clear enough. Any help would be appreciated. Thank you in advance!