我在leetcode上运行以下代码时出现运行时错误。当我删除用户定义的比较器函数时，它工作得很好。但使用用户定义的比较器函数时，会出现如下运行时错误：

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

class Solution {
public:
vector<vector<int>> groupThePeople(vector<int>& groupSizes) {
    int n = groupSizes.size();
    int visit[n];
    memset(visit, 0, sizeof(visit)); 
    vector<vector<int>>result;
    int m=0,k=0;
    for(int i=0;i<n;i++)
    {
        k=0;
        if(visit[i]!=1)
        {
            visit[i]=1;
            result[m][k]=i;
            k=1;
            for(int j=i+1;j<n;j++)
            {
                if(groupSizes[i]==groupSizes[j] && visit[j]!=1 && k+1<=groupSizes[i])
                {
                    visit[j] = 1;
                    result[m][k]=j;
                    k++;
                }
            }
            m++;
        }
        else
        {
            continue;
        }
    }
    return result;
}

};