# 203. 迷宮的最短路徑（挑戰程序設計競賽）

BFS的搜索方案是一步步擴展，天生具有搜索最短路徑性質。

``````#include <iostream>
#include <vector>
#include <queue>

using namespace std;

const int N = 110;
char arr[N][N];
int  vis[N][N];
int n, m;

int addx[4] = { 0,0,1,-1 };
int addy[4] = { 1,-1,0,0 };

int bfs(int sx, int sy) {
queue <vector<int>> q;
q.push({ sx,sy,0 });
vis[sx][sy] = 1;
while (!q.empty()) {
int currX = q.front()[0];
int currY = q.front()[1];
int step = q.front()[2];
q.pop();
//cout << currX << " " << currY  << " " << step<< endl;
for (int i = 0; i < 4; i++) {
int x = currX + addx[i];
int y = currY + addy[i];

if (x >= 0 && x < n&&y >= 0 && y < m && vis[x][y] == 0 && arr[x][y] != '#') {
if (arr[x][y] == 'G') {
return step+1;
}
q.push({x,y,step+1});
vis[x][y] = 1;
}
}
}

return -1;
}

int main() {
cin >> n >> m;
pair<int, int> start;
pair<int, int> end;
for (int i = 0; i < n; i++) {
for (int j = 0; j < m; j++) {
cin >> arr[i][j];
if (arr[i][j] == 'S') { start.first = i; start.second = j; }
}
}

cout << bfs(start.first, start.second);

return 0;
}

``````