code with run time error

this is my code when i run it and enter the input the run and after a second they throw a run time error i put some outputs to show where the problem is occur and i notice that it is occur in the function Dfs after the v reach the number 168535 but i don't know why this problem occurred...can you help me?

#include<bits/stdc++.h>

using namespace std;
typedef long l;
typedef long long ll;
typedef unsigned long long ull;
#define sc(a) scanf("%d",&a)
const int MAX = 1e6+5;
const int inf = 1e7+77;

vector<int> adj[MAX];
bool vis[MAX];
vector<int> leaf;
// 168 535 -> after this number the DFS throw run time error
void dfs(int v){
cout<<"v  =  "<<v<<endl;
leaf.push_back(v);
cout<<"running"<<endl;
vis[v] = 1;
cout<<"running"<<endl;
for(int i = 0 ; i < adj[v].size() ; ++i){
    cout<<"adj[v][i] =   "<<adj[v][i]<<endl;
    if(!vis[adj[v][i]])
        dfs(adj[v][i]);
 }
}

int main(){

int n , m , k;
sc(n);
sc(m);
sc(k);
char maze[n][m];
for(int i = 0 ; i < n ; ++i)
    for(int j = 0 ; j < m ; ++j)
        maze[i][j] = '.';
if(k > 0){
int graph[n][m];
int o = 1;
for(int i = 0 ; i < n ; ++i)
    for(int j = 0 ; j < m ; ++j){
        graph[i][j] = o;
        ++o;
    }




for(int i = 0 ; i < n ; ++i){
    for(int j = 0 ; j < m ; ++j){
        if(maze[i][j] == '.'){
            if(i + 1 < n){
                if(maze[i+1][j] == '.')
                    adj[graph[i][j]].push_back(graph[i+1][j]);
            }
            if(i - 1 >= 0){
                if(maze[i-1][j] == '.')
                    adj[graph[i][j]].push_back(graph[i-1][j]);
            }
            if(j + 1 < m){
                if(maze[i][j+1] == '.')
                    adj[graph[i][j]].push_back(graph[i][j+1]);
            }
            if(j - 1 >= 0){
                if(maze[i][j-1] == '.')
                    adj[graph[i][j]].push_back(graph[i][j-1]);
            }
        }
    }
 }

int st;
bool b = 0;
for(int i = 0 ; i < n ; ++i){
 for(int j = 0 ; j < m ; ++j){
     if(maze[i][j] == '.'){
        st = graph[i][j];
        b = 1;
    }
    if(b)
        break;
 }
 if(b)
     break;
}
cout<<"st =  "<<st<<endl;
dfs(st);


int s = leaf.size() - k;

sort(leaf.begin() + s , leaf.end());
for(int i = 0 ; i < n ; ++i){
 for(int j = 0 ; j < m ; ++j){
     if(graph[i][j] == leaf[s]){
         maze[i][j] = 'X';
         ++s;
     }
 }
}



for(int i = 0 ; i < n ; ++i){
for(int j = 0 ; j < m ; ++j)
    cout<<maze[i][j];
cout<<endl;
}
}
else
{
 for(int i = 0 ; i < n ; ++i){
 for(int j = 0 ; j < m ; ++j)
    cout<<maze[i][j];
 cout<<endl;
}
}

return 0;
}