问以下代码中的分段错误

EN

 #include <bits/stdc++.h>
using namespace std;
long long int mat[2000][2000];
int dp[2000][2000];
long long int temp[2000][2000];
int findLongestFromACell(int i, int j,int n,int m)
{
    if (i<0 || i>=n || j<0 || j>=m)
        return 0;
    if (dp[i][j] != -1)
        return dp[i][j];
    if (j<m-1 && ((temp[i][j]) == temp[i][j+1]))
      return dp[i][j] = 1 + findLongestFromACell(i,j+1,n,m);

    if (j>0 && (temp[i][j]  == temp[i][j-1]))
      return dp[i][j] = 1 + findLongestFromACell(i,j-1,n,m);

    if (i>0 && (temp[i][j]  == temp[i-1][j]))
      return dp[i][j] = 1 + findLongestFromACell(i-1,j,n,m);

    if (i<n-1 && (temp[i][j]  == temp[i+1][j]))
      return dp[i][j] = 1 + findLongestFromACell(i+1,j,n,m);
    return dp[i][j] = 1;
}

int finLongestOverAll(int n,int m,long long int p,long long int q)
{
    for(int l=0;l<n;l++)
        for(int k=0;k<m;k++)
            {
                temp[l][k] = mat[l][k];
                dp[l][k] = -1;
                if (mat[l][k]==q)
                    temp[l][k] = p;
            }
    int result = 1;
    for (int i=0; i<n; i++)
    {
      for (int j=0; j<m; j++)
      {
          if (dp[i][j] == -1)
             findLongestFromACell(i, j,n,m);
          result = max(result, dp[i][j]);
      }
     }     
     return result;
}
int main() 
{
    int n,m;
    vector <int> a;
    cin>>n>>m;
    for(int i=0;i<n;i++)
        for(int j=0;j<m;j++)
        {
            cin>>mat[i][j];
            if (find(a.begin(),a.end(),mat[i][j]) == a.end())
                a.push_back(mat[i][j]);
        }
        int l =1;
    for(int i =0;i<a.size();i++)
        for(int j=i+1;j<a.size();j++)
        {
            int m = finLongestOverAll(n,m,a[i],a[j]);
            if (m>l)
                l=m;
        }
    cout<<l;
    return 0;
}