LeetCode 695 Max Area of Island DFS

You are given an m x n binary matrix grid. An island is a group of 1's (representing land) connected 4-directionally (horizontal or vertical.) You may assume all four edges of the grid are surrounded by water.

The area of an island is the number of cells with a value 1 in the island.

Return the maximum area of an island in grid. If there is no island, return 0.

Solution

求每一块land中的最大值。我们对于每一个land进行 \(DFS\)：

点击查看代码

class Solution {
private:
    int ans = 0;
    int dir[4][2]={0,1, 1,0, -1,0, 0,-1};
    int vis[52][52];
    
    bool check(int x, int y, int r, int c){
        if(x<0||y<0||x>=r||y>=c)return false;
        return true;
    }
    
    void dfs(int x,int y, vector<vector<int>>& grid, int& cur_sum){
        if(vis[x][y]||grid[x][y]==0)return;
        if(grid[x][y]==1){
            vis[x][y] = 1;
            cur_sum+=1;
            ans=max(ans,cur_sum);
            for(int i=0;i<4;i++){
                int nx = x+dir[i][0], ny = y+dir[i][1];
                if(check(nx,ny,grid.size(),grid[0].size())){
                    dfs(nx,ny, grid,cur_sum);
                }
            }
        }
    }
    
public:
    int maxAreaOfIsland(vector<vector<int>>& grid) {
        int r = grid.size(), c = grid[0].size();
        int cur;
        for(int i=0;i<r;i++){
            for(int j=0;j<c;j++){
                if(vis[i][j]==0 && grid[i][j]==1)
                    cur = 0, dfs(i,j,grid,cur);
            }
        }
        return ans;
    }
};