[FIXED] Why getting reference binding to null-pointer error?

Issue

I am solving the following Leetcode problem:

https://leetcode.com/problems/find-if-path-exists-in-graph/

I am getting the following error:

Line 1034: Char 9: runtime error: reference binding to null pointer of type 'std::vector<int, std::allocator<int>>' (stl_vector.h)
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior /usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../include/c++/9/bits/stl_vector.h:1043:9

The code for my approach:

class Solution {
public:
    void dfs(int *visited,int node,vector<vector<int>>&adj)
    {
        visited[node]=1;
        for(auto child:adj[node])
        {
            if(visited[child]==-1)
                dfs(visited,child,adj);
        }
    }
    bool validPath(int n, vector<vector<int>>& edges, int source, int destination) {
        vector<vector<int>>adj;
        for(auto it:edges)
        {
            adj[it[0]].push_back(it[1]);
            
        }
        int visited[n];
        for(int i=0;i<n;i++)
            visited[i]=-1;
        
        dfs(visited,source,adj);
        
        return visited[destination]==1;
    }
};

I'm getting this error for almost every graph problem. Can someone point out the mistake?

Solution

The outer vector of adj should be resized, before adding elements to the inner vector.

bool validPath(int n, vector<vector<int>>& edges, int source, int destination) {
    vector<vector<int>>adj;
    for(auto& it:edges)
    {
        if (adj.size() < (it[0] + 1))
        {
            adj.resize(it[0] + 1);    
        }
        
        adj[it[0]].push_back(it[1]);
            
    }
    
    //Rest of the code  
}

Answered By - ruvenij

Answer Checked By - Mildred Charles (PHPFixing Admin)