bfs_grid

#include "bits/stdc++.h"

using namespace std;

const int maxN = 100;
bool visited[maxN][maxN];
int cost[maxN][maxN];
pair<int,int> parent[maxN][maxN];

char grid[maxN][maxN];

int dx[4] = {1, 0, -1, 0};
int dy[4] = {0, 1, 0, -1};

void bfs (int x,int y, int n, int m) {
	queue<pair<int,int>> q;
	q.push(make_pair(x, y));
	cost[x][y] = 0;
	visited[x][y] = true;
	while (!q.empty()) {
		pair<int,int> u = q.front();
		q.pop();
		for (int i = 0; i < 4; ++i) {
			int dxx = dx[i] + u.first;
			int dyy = dy[i] + u.second;
			if (dxx >= 1 and dxx <= n and dyy >= 1 and dyy <= m and grid[dxx][dyy] != '#' and !visited[dxx][dyy]) {
				visited[dxx][dyy] = true;
				cost[dxx][dyy] = cost[u.first][u.second] + 1;
				q.push(make_pair(dxx, dyy));
				parent[dxx][dyy] = u;
			}
		}
	}
}

int main () {
	 int n, m;
	 cin >> n >> m;
	 int xx, yy, x, y;
	 for (int i = 1; i <= n; ++i) {
		 for (int j = 1; j <= m; ++j) {
			 cin >> grid[i][j];
			 if (grid[i][j] == 'A') {
				 x = i, y = j;
			 }
			 if (grid[i][j] == 'B') {
				 xx = i, yy = j;
			 }
		 }
	 }
	 bfs(x, y, n, m);
	 cout << cost[xx][yy] << '\n';
}