释放动态分配的内存时程序崩溃

我在这里使用邻接列表来表示一个图。

这是代码：

// A program to check the reachability between two nodes within a specified number of steps using an adjacency list
/***************************************************************************/
#include <iostream>
#include <fstream>
using namespace std;
struct node {
    int value;
    node* next;
    // Constructors:
    node() {
        value = 0;
        next = 0;
    }
    node(int x) {
        value = x;
        next = 0;
    }
};

node* al; // Adjacency list
int n; // Number of nodes
int node1, node2, k; // For reading input from the console
int counter;
bool checkReachability(int, int, int);
void freeMemory();
int main() {
    ifstream in;
    in.open("Input.txt");
    if(in) {
        in >> n;
        al = new node[n];
        for (int i = 0; i < n; i++) {
            al[i].value = i+1;
        }
        int a, b;
        while(in >> a >> b) {
            node* temp = &al[a-1];
            while(temp->next != 0) {
                temp = temp->next;
            }
            temp->next = new node(b);    
        }
        cout << "nnThe adjacency list representation of the graph is as follows: n";
        cout << "________________________________nn";
        for (int i = 0; i < n; i++) {
            cout << al[i].value;
            node* temp = al[i].next;
            while(temp != 0) {
                cout << "->" << temp->value;
                temp = temp->next;
            }
            cout << endl;
        }
        cout << "________________________________n";
        in.close();
        char c;
        do {
            cout << "nPlease enter the input (node1, node2, k): n";
            cin >> node1 >> node2 >> k;
            counter = 0;
            if (checkReachability(node1 - 1, node2, k)) {
                cout << "nReachable within " << k << " steps";
                if (counter < k) {
                    cout << " (actually " << counter << ")";
                }
                cout << endl << endl;
            }
            else {
                cout << "nNot reachable within " << k << " steps  n";
            }
            cout << "nDo you want to continue? Y/N nn";
            cin >> c;
        } while (c == 'Y' || c == 'y');
        freeMemory();
    } else {
        cout << "nCouldn't find the input filenn";
    }
    return 0;
}
bool checkReachability(int n1, int n2, int k) {
    if ((n1 + 1) == n2) return true;
    counter++;
    if (counter <= k) {
        node* temp = &(al[n1]);
        while (temp != 0) {
            if (temp->value == n2) return true;
            temp = temp->next;
        }
        temp = al[n1].next; 
        while (temp != 0) {
            if (checkReachability(((temp->value)-1),n2,k)) return true;
            counter--;
            temp = temp->next;
        }   
    }
    return false;
}
void freeMemory() {
    cout << "nFreeing memory...n";
    // To free the dynamically allocated memory on the heap
    for (int i = 0; i < n; i++) {
        node* temp = &al[i];
        while(temp != 0) {
            node* temp2 = temp;
            temp = temp->next;
            delete temp2;
        }
    }
    //delete [] al;
    cout << "nMemory freed.n";
}

这个程序运行得很好。只有当我选择退出它时，它才会崩溃，因为它调用了freeMemory函数。请帮我弄清楚问题出在哪里。

Input.txt文件：

5
1 2
2 5
3 4
1 3

输出：

The adjacency list represent
____________________________
1->2->3
2->5
3->4
4
5
____________________________
Please enter the input (node
1 2 1
Reachable within 1 steps

Do you want to continue? Y/N
y
Please enter the input (node
2 4 4
Not reachable within 4 steps
Do you want to continue? Y/N
N
Freeing memory...

然后，它崩溃了。