HackerEarth Nodes in a subtree problem solution

In this HackerEarth Nodes in a subtree problem solution, You are given a rooted tree that contains N nodes. Each node contains a lowercase alphabet.

You are required to answer Q queries of type u,c, where u is an integer and c is a lowercase alphabet. The count of nodes in the subtree of the node u containing c is considered as the answer of all the queries. 

#include<bits/stdc++.h>
using namespace std;
int cnt[100005][26], n;
vector<int> adj[100005];
string s;
void dfs(int u, int parent)
{
    int i;
    for(i = 0; i < 26; i ++)
    cnt[u][i] = 0;
    cnt[u][s[u - 1] - 'a'] ++;
    for(auto v: adj[u])
    {
        if(v == parent)
        continue;
        dfs(v, u);
        for(i = 0; i < 26; i ++)
        cnt[u][i] += cnt[v][i];
    }
}
int main()
{
    int q, i;
    cin >> n >> q;
    cin >> s;
    for(i = 0; i < n - 1; i ++)
    {
        int u, v;
        cin >> u >> v;
        adj[u].push_back(v);
        adj[v].push_back(u);
    }
    dfs(1, 0);
    while(q --)
    {
        int u;
        char c;
        cin >> u >> c;
        cout << cnt[u][c - 'a'] << endl;
    }
    return 0;
}