HackerEarth Minimum cost problem solution

#include <bits/stdc++.h>
using namespace std;

const int maxn = 1e5 + 17;
int n, d[maxn], p[maxn];
bool mark[maxn];
int main(){
    ios::sync_with_stdio(0), cin.tie(0);
    int t;
    cin >> t;
    while(t--){
        cin >> n;
        for(int i = 0; i < n; i++)
            cin >> p[i], p[i]--;
        fill(d + 1, d + n, n);
        memset(mark, 0, sizeof mark);
        queue<int> q({0});
        while(q.size()){
            int i = q.front();
            q.pop();
            if(mark[i])
                continue;
            mark[i] = 1;
            vector<int> self({i});
            while(p[self.back()] != i){
                self.push_back(p[self.back()]);
                d[self.back()] = d[i];
                mark[self.back()] = 1;
            }
            auto add = [&](int j){
                if(d[j] <= d[i] + 1)
                    return ;
                d[j] = d[i] + 1;
                q.push(j);
            };
            for(auto i : self){
                if(i)
                    add(i - 1);
                if(i < n - 1)
                    add(i + 1);
            }
        }
        cout << d[n - 1] << 'n';
    }
}