200.岛屿数量 (Medium)*

题目描述*

给定一个由 '1'（陆地）和 '0'（水）组成的的二维网格，计算岛屿的数量。一个岛被水包围，并且它是通过水平方向或垂直方向上相邻的陆地连接而成的。你可以假设网格的四个边均被水包围。

示例*

输入:

输出: 1

输入:

输出: 3

代码*

dfs 或 bfs 即可。还可以用并查集，过段时间学一下。

dfsbfs

class Solution {
public:
    int numIslands(vector<vector<char>>& grid) {
        int cnt = 0;
        int rows = grid.size();
        if(rows == 0) {
            return 0;
        }
        int cols = grid[0].size();
        for(int i = 0; i < rows; i++) {
            for(int j = 0; j < cols; j++) {
                if(grid[i][j] == '1') {
                    dfs(grid, i, j);
                    cnt++;
                }
            }
        }
        return cnt;
    }
    void dfs(vector<vector<char>>& grid, int i, int j) {
        if(i < 0 || j < 0 || i >= grid.size() || j >= grid[0].size() || grid[i][j] != '1') {
            return;
        }
        grid[i][j] = '2';
        dfs(grid, i + 1, j);
        dfs(grid, i - 1, j);
        dfs(grid, i, j + 1);
        dfs(grid, i, j - 1);
    }
};

class Solution {
public:
    int numIslands(vector<vector<char>>& grid) {
        int cnt = 0;
        int rows = grid.size();
        if(rows == 0) {
            return 0;
        }
        int cols = grid[0].size();
        for(int i = 0; i < rows; i++) {
            for(int j = 0; j < cols; j++) {
                if(grid[i][j] == '1') {
                    bfs(grid, i, j, rows, cols);
                    cnt++;
                }
            }
        }
        return cnt;
    }
    void bfs(vector<vector<char>>& grid, int i, int j, int rows, int cols) {
        queue<int> helpQueue;
        helpQueue.push(i * cols + j);
        while(!helpQueue.empty()) {
            int cur = helpQueue.front();
            helpQueue.pop();
            int row = cur / cols;
            int col = cur % cols;
            if(grid[row][col] == '2') {
                continue;
            }
            grid[row][col] = '2';
            if(row != rows - 1 && grid[row + 1][col] == '1') {
                helpQueue.push((row + 1) * cols + col);
            }
            if(col != cols - 1 && grid[row][col + 1] == '1') {
                helpQueue.push(row * cols + col + 1);
            }
            if(row != 0 && grid[row - 1][col] == '1') {
                helpQueue.push((row - 1) * cols + col);
            }
            if(col != 0 && grid[row][col - 1] == '1') {
                helpQueue.push(row * cols + col - 1);
            }
        }
    }
};

最后更新: July 23, 2022