LEETCODE- -NUMBER OF ISLANDS--RUNTIME ERROR

1

WHY MY CODE IS GIVING ERROR >>>Line 924: Char 9: runtime error: reference binding to null pointer of type ‘std::vector<char, std::allocator >’ (stl_vector.h)

class Solution {
public:
   


  
  
  void dfs(vector<vector<char>> &grid,int i,int j,int n,int m)  
  {
      if(i<0 || j<0|| i>=n||j>=m || grid[i][j]=='0'|| grid[i][j]=='v')
      {
          return ;
      }
   
      grid[i][j]='v';
      dfs( grid, i+1, j, n, m);
      dfs( grid, i-1, j, n, m);
      dfs( grid, i, j+1, n, m);
      dfs( grid, i, j-1, n, m);
  
  
  
  
  }
    
    
        int numIslands(vector<vector<char>>& grid)
    {
     int n=grid.size();
     int m=grid[0].size();
        int ans=0;
        for(int i=0;i<n;i++)
        {  for(int j=0;j<m;j++)
           {
               if( grid[i][j]=='1')
               {
                   ans++;
                   dfs( grid, i, j, n, m);
               }
        
          }
        }
        return ans;
    }
    

    
    

};


please help >>> @everule1  @ssjgz @galencolin @vijju123
2

can’t see the code, page not found

I’m not familiar with this runtime error message, but a good trick when the compiler actually tells you something is to look up your exact error - chances are someone else has also faced it before.

1 Like
3

I HAVE REMOVED THE LINK AND ADDED THE CODE SO,CAN YOU PLEASE TELL ME THE ERROR…??

4

your void dfs function is wrong…that why you get runtime error…
try this …
( you can replace grid.size()by n and grid[0].size()by m)

void dfs(vector<vector<char>>& grid,int i,int j){
    grid[i][j]='0';
    if(i-1>=0 && grid[i-1][j]=='1'){
        dfs(grid,i-1,j);
    }
    if(j-1>=0 && grid[i][j-1]=='1'){
        dfs(grid,i,j-1);
    }
    if(i+1<grid.size() && grid[i+1][j]=='1'){
        dfs(grid,i+1,j);
    }
    if(j+1<grid[0].size() && grid[i][j+1]=='1'){
        dfs(grid,i,j+1);
    }
    
}

if still have problem then watch this solution video
explanation

1 Like
5

thank you i spotted the error >>>the value of columns can be diffrent i shoold have iterated j from 0 tiogrid [i].size() not grid[0].size() …