Leetcode Number of Islands problem solution

def numIslands(self, grid):
        def dfs(x, y):
            if x < 0 or x >= len(grid) or y < 0 or y >= len(grid[0]) or grid[x][y] != '1':
                return
            grid[x][y] = '0'
            for i, j in [(x - 1, y), (x, y - 1), (x + 1, y), (x, y + 1)]:
                dfs(i, j)
        
        if not grid or not grid[0]:
            return 0
        res = 0
        for i in range(len(grid)):
            for j in range(len(grid[0])):
                if grid[i][j] == '1':
                    dfs(i, j)
                    res += 1
        return res

class Solution {
    public int numIslands(char[][] grid) {
        if (grid == null || grid.length == 0 || grid[0].length == 0)
            return 0;
        int r = grid.length;
        int c = grid[0].length;
        int res = 0;
        for (int i = 0; i < r; i++) {
            for (int j = 0; j < c; j++) {
                if (grid[i][j] == '1') {
                    dfs(grid, i, j);
                    res++;
                }
            }
        }
        return res;
    }
    
    private void dfs(char[][] grid, int r, int c) {
        int rowNum = grid.length;
        int colNum = grid[0].length;
        if (r < 0 || r >= rowNum || c < 0 || c >= colNum || grid[r][c] == '0') {
            return;
        }
        grid[r][c] = '0';
        dfs(grid, r + 1, c);
        dfs(grid, r - 1, c);
        dfs(grid, r, c + 1);
        dfs(grid, r, c - 1);
    }
}

class Solution {
public:
    int row, col;
    void dfs(vector<vector<char>> & grid, int y, int x){
        if(y < 0 || x < 0 || y >= row || x >= col || grid[y][x] != '1')
            return ;
        grid[y][x] = '#';
        dfs(grid, y + 1, x);
        dfs(grid, y - 1, x);
        dfs(grid, y, x - 1);
        dfs(grid, y, x + 1);
    }
    int numIslands(vector<vector<char>>& grid) {
        row = grid.size();
        if(!row) return 0;
        col = grid[0].size();
        int count = 0;
        for(int i = 0; i < row; i++){
            for(int j = 0; j < col; j++){
                if(grid[i][j] == '1'){
                    dfs(grid, i, j);
                    count++;
                }
            }
        }
        return count;
    }
};

int label(char** grid,int row,int col,int gridRowSize, int gridColSize );
int numIslands(char** grid, int gridRowSize, int gridColSize) {
    int row,col;
    int newlabel;
    newlabel=0;
    for(row=0;row<=gridRowSize-1;row++)
    {
       for(col=0;col<=gridColSize-1;col++) 
       {
           newlabel=newlabel+label(grid,row,col,gridRowSize,gridColSize);
       }
        
    }
    
    return newlabel;
}

int label(char** grid,int row,int col,int gridRowSize, int gridColSize )
{
    if (*(*(grid+row)+col)=='1')
    {
        *(*(grid+row)+col)='0';
        if (row!=0)
            label(grid,row-1,col,gridRowSize,gridColSize );
        if (row!=gridRowSize-1)    
            label(grid,row+1,col,gridRowSize,gridColSize );
        if (col!=0)
            label(grid,row,col-1,gridRowSize,gridColSize );
        if (col!=gridColSize-1)    
            label(grid,row,col+1,gridRowSize,gridColSize ); 
        
        return 1;
    }
    else    
        return 0;
  
}