# Writing your custom sort functions in C++

** Published:**

In this blog post I will quickly go over how to define your custom comparator for `sort()`

for your data structure in C++ based on two example cases.

I decided to start programming in C++ again after a long time (end of 2017!!) because I was practising algorithm-style problems for job interviews and C++ seemed like a natural choice. It’s Standard Template Library makes working with data structures very easy by providing a uniform api and inbuild data structures. I noticed that a lot of the questions that I came across required me to overload the comparator operator in C++ `sort()`

function since I was working with custom data structures. Next, I will mention two example cases of such problems and how I went around writing the sort comparator for my requirements.

# Case 1. Sort a `vector<vector<int>>`

based on two different conditions

```
struct contestComparator
{
bool operator ()(const vector<int> & contest1, const vector<int> & contest2)
{
if(contest1[1] != contest2[1])
return contest1[1] > contest2[1]; // consider important contests first
return contest1[0] < contest2[0];
}
};
// Complete the luckBalance function below.
int luckBalance(int k, vector<vector<int>> contests) {
int luck_balance = 0;
int len = contests.size();
sort(contests.begin(), contests.end(), contestComparator());
int num_important = 0;
for(int i = 0; i<len && contests[i][1] == 1; i++)
num_important++;
k = num_important - k;
for(int i = 0; i < len; i++)
{
cout<<contests[i][0]<<" ";
if(i<k)
luck_balance -= contests[i][0];
else
luck_balance += contests[i][0];
}
return luck_balance;
}
```

# Case 1. Sort a `vector<pair<int, int>>`

based on the first number in the `pair`

```
struct pairComp
{
bool operator ()(const pair<int, int> & pair1, const pair<int, int> & pair2)
{
return pair1.first < pair2.first;
}
};
// Complete the whatFlavors function below.
void whatFlavors(vector<int> cost, int money) {
vector<pair<int,int>> costidx;
for(int i=0; i<cost.size(); i++)
costidx.push_back(make_pair(cost[i], i+1));
sort(costidx.begin(), costidx.end());
int i=0;
int j=cost.size()-1;
while(i<j)
{
if(costidx[i].first + costidx[j].first > money)
j--;
else if(costidx[i].first + costidx[j].first < money)
i++;
else
break;
}
int min = (costidx[i].second < costidx[j].second)? costidx[i].second:
costidx[j].second;
int max = (costidx[i].second > costidx[j].second)? costidx[i].second:
costidx[j].second;
cout<<min<<" "<<max<<endl;
}
```