力扣剑指offer2第36天图

105）岛屿的最大面积

dfs

class Solution{
public:
    int maxAreaOfIsland(vector<vector<int>>& grid){
        int res = 0;
        int m = grid.size(), n = grid[0].size();
        for(int i=0; i<m; i++){
            for(int j=0; j<n; j++){
                if(grid[i][j]==1){
                    res = max(res, dfs(grid, i, j));
                }
            }
        }
        return res;
    }
    
    int dfs(vector<vector<int>>& grid, int i, int j){
        int m = grid.size(), n = grid[0].size();
        if(i<0 || j<0 || i>=m || j>=n) return 0;
        if(grid[i][j]==0) return 0;
        grid[i][j]=0;
        return dfs(grid, i+1, j) + dfs(grid, i-1, j) + dfs(grid, i, j+1) + dfs(grid, i, j-1) + 1;
    }
};

106)判断二分图

class Solution{
private:
    bool ok=true;
public:
    bool isBipartite(vector<vector<int>>& graph){
        int n = gragh.size();
        vector<bool> visit(n, false);
        vector<bool> color(n, false);
        for(int v=0; v<n; v++){
            if(!visit[v]){
                traverse(graph, v, visit, color);
            }
        }
        return ok;
    }
    void traverse(vector<vector<int>>& graph, int v, vector<bool>& visit, vector<bool>& color){
        if(!ok) return;
        visit[v] = true;
        for(int w : graph[v]){
            if(!visit[w]){
                color[w] = !color[v];
                traverse(graph, w, visit, color);
            }else{
                if(color[w] == color[v]){
                    ok = false;
                }
            }
        }
    }
};

107)矩阵中的距离

class Solution{
private:
    int dir[4][2] = {{0, 1}, {0, -1}, {-1, 0}, {1, 0}};
public:
    vector<vector<int>> updateMatrix(vector<vector<int>>& mat){
        int m=mat.size(), n=mat[0].size();
        vector<vector<int>> dist(m, vector<int>(n));
        vector<vector<int>> seen(m, vector<int>(n));
        queue<pair<int, int>> q;
        for(int i=0; i<m; i++){
            for(int j=0; j<n; j++){
                if(mat[i][j]==0){
                    q.emplace(i, j);
                    seen[i][j] = 1;
                }
            }
        }
        while(!q.empty()){
            auto [i, j] = q.front();
            q.pop();
            for(int d=0; d<4; d++){
                int ni = i + dir[d][0];
                int nj = j + dir[d][1];
                if(ni>=0 && nj>=0 && ni<m && nj<n && !seen[ni][nj]){
                    dist[ni][nj] = dist[i][j] + 1;
                    q.emplace(ni, nj);
                    seen[ni][nj] = 1;
                }
            }
        }
        return dist;
    }
};