Free() invalid pointer error in C++

I wrote this C++ program but I got the following error:

*** Error in `/home/max4/Data/Programming/youcandoit/bin/Debug/youcandoit': free(): invalid pointer: 0x0000000000de2030 ***
Aborted

I was trying to solve this problem.

If anyone could help point out what mistakes I've made or if there are any clarifications that I can make for you, please leave a comment below.

Thanks, Max.

The following is my code.

#include <bits/stdc++.h>
#define dist second
#define key first
using namespace std;

int driver();
vector<int> inttovec(int);
int vectoint(vector<int>);
int bfs(int);
int value;
vector<int> stacks[8];

int n;

int bfs(int state) {
    bitset<823543+2> vis;
    vis.reset();
    queue<pair<int, int>> qu; ///first is key second is dist
    qu.push(make_pair(state, 0));
    while (!qu.empty()) {
        auto cur = qu.front(); qu.pop();
        if (cur.key == value) return cur.dist;
        vis[cur.key] = true;
        vector<int> vcur = inttovec(cur.key);
        printf("currently at ");
        for (int i=0; i<n; ++i) printf("%d ", vcur[i]);
        printf("\n");

        for (int i=0; i<n; ++i) {
            stacks[i].clear();
        }
        for (int i=0; i<n; ++i) {
            stacks[vcur[i]].push_back(i);
        }

        for (int pos=0; pos<n; ++pos) {
            if (stacks[pos].empty()) continue;
            for (int to=max(0, pos-1); to<=min(n-1, pos+1); ++to) {
                if (to == pos || !stacks[to].empty() && stacks[to][0] < stacks[pos][0]) continue;
                vcur[stacks[pos][0]] = to; ///change
                int newstate = vectoint(vcur); ///int-ify change
                if (!vis[newstate]) {
                    printf("\tmove coin %d from pos %d to pos %d\n", stacks[pos][0], pos, to);
                    printf("\tto ");
                    for(int i=0; i<n; ++i) printf("%d ", vcur[i]);
                    printf("\n");
                }
                vcur[stacks[pos][0]] = pos; ///undo change
                if (!vis[newstate]) {
                    qu.push(make_pair(newstate, cur.dist+1));
                    vis[newstate] = true;
                }
            }
        }
    }
    printf("reached end of control\n");
    return -1;
}

int vectoint(vector<int> vec2) {
    int ret = 0;
    for (int i=0; i<n; ++i) { ///technically this uses little endian instead of big or smth, but hey! go screw urself.
        ret += (int)pow(n, i)*vec2[i];
    }
    return ret;
}

vector<int> inttovec(int num) {
    vector<int> ret;
    for (int i=n-1; i>=0; --i) {
        //printf("%d: %d/pow = %d\n", i, num, num/(int)pow(n, i));
        ret.push_back(num/(int)pow(n, i));
        num %= (int) pow(n, i); /// could this ever be 0? probably not.
    }
    reverse(ret.begin(), ret.end());
    return ret;
}

int driver() {
    vector<int> positions(n);
    int tmp;
    for (int i=0; i<n; ++i) {
        scanf("%d", &tmp); --tmp;
        positions[tmp] = i;
    }
    int state = vectoint(positions);
    int ans = bfs(state);
    return ans;
}

int main()
{
    freopen("test.txt", "r", stdin);
    scanf("%d", &n);
    vector<int> should;
    for (int i=0; i<n; ++i) {
        should.push_back(i);
    }
    value = vectoint(should);
    printf("value %d\n", value);
    for (auto i:inttovec(5)) {
        cout << i << " ";
    }
    cout << endl;

    while (n != 0) {
        int ans = driver();
        if (ans == -1) printf("IMPOSSIBLE\n");
        else printf("%d\n", ans);
        scanf("%d", &n);
    }
}