深度与广度优先搜索学习（基于LeetCode第130题被围绕的区域）

代码简单易懂，直接上：

广度优先搜索：

#include<iostream>
#include<string>
#include<vector>
#include<set>
#include<unordered_set>
#include<unordered_map>
#include<queue>

using namespace std;

class Solution {
public:
    //x坐标与y坐标的偏移量，同步的话即各往上下左右走一步
    const int dx[4] = {1, -1, 0, 0};
    const int dy[4] = {0, 0, 1, -1};

    void solve(vector<vector<char>>& board) {
        int n = board.size();
        if (n == 0) {
            return;
        }
        int m = board[0].size();

        queue<pair<int, int>> que;
        //边界在插进队列的时候已经把O变成A了！
        for (int i = 0; i < n; i++) {
            if (board[i][0] == 'O') {
                que.emplace(i, 0);
                board[i][0] = 'A';
            }
            if (board[i][m - 1] == 'O') {
                que.emplace(i, m - 1);
                board[i][m - 1] = 'A';
            }
        }
        for (int i = 1; i < m - 1; i++) {
            if (board[0][i] == 'O') {
                que.emplace(0, i);
                board[0][i] = 'A';
            }
            if (board[n - 1][i] == 'O') {
                que.emplace(n - 1, i);
                board[n - 1][i] = 'A';
            }
        }
        while (!que.empty()) {
            int x = que.front().first, y = que.front().second;
            que.pop();
            for (int i = 0; i < 4; i++) {
                int mx = x + dx[i], my = y + dy[i];
                if (mx < 0 || my < 0 || mx >= n || my >= m || board[mx][my] != 'O') {
                    continue;
                }
                que.emplace(mx, my);
                board[mx][my] = 'A';
            }
        }
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
                if (board[i][j] == 'A') {
                    board[i][j] = 'O';
                } else if (board[i][j] == 'O') {
                    board[i][j] = 'X';
                }
            }
        }
    }
};

int main() {
    vector<vector<char>> board;
    vector<char> smallBoard;
    int n;
    cin >> n;
    char tmp;
    for(int i=0;i<n;i++){
        for(int j=0;j<n;j++){
            cin>>tmp;
            smallBoard.emplace_back(tmp);
        }
        board.emplace_back(smallBoard);
        smallBoard.clear();
    }
    Solution sol;
    sol.solve(board);
    for(int i=0;i<n;i++){
        for(int j=0;j<n;j++)
            cout<<board[i][j]<<" ";
        cout << endl;
    }
    return 0;
}
/**
输入:
4
X X X X
X O O X
X X O X
X O X X
输出:
X X X X
X X X X
X X X X
X O X X
*/

深度优先搜索：

#include<iostream>
#include<string>
#include<vector>
#include<set>
#include<unordered_set>
#include<unordered_map>
#include<queue>

using namespace std;

class Solution {
public:
    int n, m;

    void dfs(vector<vector<char>> &board, int x, int y) {
        if (x < 0 || x >= n || y < 0 || y >= m || board[x][y] != 'O') {
            return;
        }
        board[x][y] = 'A';
        dfs(board, x + 1, y);
        dfs(board, x - 1, y);
        dfs(board, x, y + 1);
        dfs(board, x, y - 1);
    }

    void solve(vector<vector<char>> &board) {
        n = board.size();
        if (n == 0) {
            return;
        }
        m = board[0].size();

        for (int i = 0; i < n; i++) {
            dfs(board, i, 0);
            dfs(board, i, m - 1);
        }

        for (int i = 1; i < m - 1; i++) {
            dfs(board, 0, i);
            dfs(board, n - 1, i);
        }

        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
                if (board[i][j] == 'A') {
                    board[i][j] = 'O';
                } else if (board[i][j] == 'O') {
                    board[i][j] = 'X';
                }
            }
        }
    }
};

int main() {
    vector<vector<char>> board;
    vector<char> smallBoard;
    int n;
    cin >> n;
    while (n--) {
        char tmp;
        while (1) {
            cin >> tmp;
            if (tmp == 'Z')
                break;
            smallBoard.emplace_back(tmp);
        }
        board.emplace_back(smallBoard);
        smallBoard.clear();
    }
    Solution sol;
    sol.solve(board);
    for (auto i:board) {
        for (auto j:i) {
            cout << j << " ";
        }
        cout << endl;
    }
    return 0;
}
/** 
输入:
4
X X X X Z
X O O X Z
X X O X Z
X O X X Z
输出:
X X X X
X X X X
X X X X
X O X X
*/

我是花花，祝自己也祝您变强了~