岛屿面积问题

1.岛屿的最大面积

class Solution {
public:
    int maxAreaOfIsland(vector<vector<int>>& grid) {
        if(grid.size()==0)return 0;
        int n=grid.size();
        int m=grid[0].size();
        int max=0;
        vector<vector<bool>>visited(n,vector<bool>(m,false));
        for(int i=0;i<n;i++){
            for(int j=0;j<m;j++){
                if(grid[i][j]==1&&visited[i][j]==false){
                    int tmp=cal_area(grid,i,j,n,m,visited);
                    max=tmp>max?tmp:max;
                }
            }
        }
        return max;
    }
    int cal_area(vector<vector<int>>& grid,int i,int j,int rows,int cols,vector<vector<bool>>&visited){
        if(i>=0&&i<rows&&j>=0&&j<cols&&grid[i][j]==1&&visited[i][j]==false){
            visited[i][j]=true;
            return 1+cal_area(grid,i+1,j,rows,cols,visited)+cal_area(grid,i-1,j,rows,cols,visited)+cal_area(grid,i,j-1,rows,cols,visited)
                +cal_area(grid,i,j+1,rows,cols,visited);
        }
        else{
            return 0;
        }
    }
};

2.岛屿的个数

class Solution {
public:
    int numIslands(vector<vector<char>>& grid) {
        if (grid.empty() || grid[0].empty()) return 0;
        int n=grid.size();
        int m=grid[0].size();
        vector<vector<bool>>visited(n,vector<bool>(m,false));
        int res=0;
      for (int i = 0; i < n; ++i) {
            for (int j = 0; j < m; ++j) {
                if (grid[i][j] == '1' && !visited[i][j]) {
                    help(grid,i,j,n,m,visited);
                    ++res;
                }
            }
        }
        return res;   
    }
    
    void help(vector<vector<char> > &grid,  int x, int y, int n,int m,vector<vector<bool>>&visited) {
    if (x >= 0 && x < n&& y >= 0 && y < m && grid[x][y] == '1' && visited[x][y] == false){
        visited[x][y] = true;
        help(grid, x - 1, y, n, m, visited);
        help(grid, x + 1, y, n, m, visited);
        help(grid, x, y - 1, n, m, visited);
        help(grid, x, y + 1, n, m, visited);
        }
    
    }
};