#include <bits/stdc++.h>
using namespace std;
void radixsort(vector<pair<pair<int, int>, int>> &a)
{
    int n = a.size();
    {
        vector<int> cnt(n);
        for (auto x : a)
        {
            cnt[x.first.second]++;
        }
        vector<pair<pair<int, int>, int>> a_new(n);
        vector<int> pos(n);
        pos[0] = 0;
        for (int i = 1; i <= n; ++i)
        {
            pos[i] = pos[i - 1] + cnt[i - 1];
        }
        for (auto x : a)
        {
            int i = x.first.second;
            a_new[pos[i]] = x;
            pos[i]++;
        }
        a = a_new;
    }
    {
        vector<int> cnt(n);
        for (auto x : a)
        {
            cnt[x.first.first]++;
        }
        vector<pair<pair<int, int>, int>> a_new(n);
        vector<int> pos(n);
        pos[0] = 0;
        for (int i = 1; i <= n; ++i)
        {
            pos[i] = pos[i - 1] + cnt[i - 1];
        }
        for (auto x : a)
        {
            int i = x.first.first;
            a_new[pos[i]] = x;
            pos[i]++;
        }
        a = a_new;
    }
}
int main()
{
    string s;
    cin >> s;
    s += "$";
    int n = s.size();
    vector<int> p(n), c(n);
    {
        vector<pair<char, int>> a(n);
        for (int i = 0; i < n; ++i)
        {
            a[i] = {s[i], i};
        }
        sort(a.begin(), a.end());
        for (int i = 0; i < n; ++i)
        {
            p[i] = a[i].second;
        }
        c[p[0]] = 0;
        for (int i = 1; i < n; ++i)
        {
            if (a[i].first == a[i - 1].first)
            {
                c[p[i]] = c[p[i - 1]];
            }
            else
            {
                c[p[i]] = c[p[i - 1]] + 1;
            }
        }
    }
    int k = 0;
    while ((1 << k) < n)
    {
        vector<pair<pair<int, int>, int>> a(n);
        for (int i = 0; i < n; ++i)
        {
            a[i] = {{c[i], c[(i + (1 << k)) % n]}, i};
        }
        radixsort(a);
        for (int i = 0; i < n; ++i)
        {
            p[i] = a[i].second;
        }
        c[p[0]] = 0;
        for (int i = 1; i < n; ++i)
        {
            if (a[i].first == a[i - 1].first)
            {
                c[p[i]] = c[p[i - 1]];
            }
            else
            {
                c[p[i]] = c[p[i - 1]] + 1;
            }
        }
        k++;
    }
    for (int i = 0; i < n; ++i)
    {
        cout << p[i] << ' ';
    }
    return 0;
}

All of the probable error will be in the function called radixsort ,the other part doesn't have any error.

Could anyone tell me where the error is?

The original code could be found in the Suffix Array of the edu.