c++ map根据value排序以及lamda表达式的应用

vector<int> topKFrequent(vector<int>& nums, int k) {
map<int, int> m;
vector<pair<int, int>> temp;
vector<int> res;
for (auto n : nums) {
m
++;
}
for (auto i : m) {
temp.push_back(i);
}
std::sort(temp.begin(), temp.end(), [](pair<int, int>& a, pair<int, int>& b) {return a.second > b.second;});
for (auto i:temp) {
res.push_back(i.first);
k--;
if (k == 0) return res;
}
}