1166A-Silent Classroom

#include <iostream>

#include<vector>

#include<string>

#include<math.h>

#include<set>

#include<map>

#include<stack>

#include<queue>

#include<algorithm>

/* ==================================================

  |                                                  |

  |    Author: *** S. M. Sabiul Hajjaj Sabit ***     |

  |       Last Edit:  May,14,2019                    |

   ================================================== */

///***global declaration***///

#define all(arr) arr.begin(),arr.end()

#define pb push_back

#define sz(x) x.size()

#define min3(a,b,c)  min(min(a,b),c)

#define max3(a,b,c)  max(max(a,b),c)

using namespace std;

int i,j,n,m,sum=0,ans=0;

template <typename T>long long int power(T a, T b)

{

    long long int pow=1;

    for(int i=0; i<b; i++)

    {

        pow *= a;

    }

    return pow;

}

///*********Write Code From Here*********///

int main()

{

    vector<int>arr(26,0);

    int count=0;

    cin>>n;

    //cout<<power(3,1)<<endl;

    for(int i=0; i<n; i++)

    {

        string s;

        cin>>s;

        int t = s[0]-97;

        arr[t]++;

    }

    for(int i=0; i<26; i++)

    {

        int k = arr[i]/2;

        int l = arr[i]-k;

        // cout<<( k - 1) * k / 2<<" "<< ( l - 1) * l / 2<<arr[i]<<endl;

        count  = (count  + ( k - 1) * k / 2);

        count = (count + ( l - 1) * l / 2);

        //  cout<<count<<endl;

    }

    cout<<count<<endl;

}