广度优先搜索--迷宫最短路径--队列

不同于深度优先遍历，先找一个子节点，再找子节点的子节点...

广度优先遍历会挨着子节点遍历，第一层的子节点遍历完了，才会遍历第二层；如图：

bfs(起点){
起点加入队列；
while (队列!=空) {
得到队首x；
删除队首;
for(遍历X的子节点){
子节点加入队列尾；
}
}
}



所以说，用广度优先 先访问到的目标一定是 层数最少的--路径最短的；

所以走迷宫求最短路径可以这么写：

#代表障碍物，S代表起点；T代表中点；

其中最短路径可以用结点的路径来记录；

public class 走迷宫最小步数 {

static String map[];
static boolean[][] visit;
static int dir[][] = {{1, 0}, {0, 1}, {-1, 0}, {0, -1}}; //对应的上下左右4各方向
static int n;
static int m;
public static void main(String[] args) {
// TODO Auto-generated method stub
Scanner input = new Scanner(System.in);
n = input.nextInt();
m = input.nextInt();
map = new String
;
visit = new boolean
[m];
for (int i = 0; i < n; i++) {
map[i] = input.next();
}
int x = 0, y = 0;
for (int i = 0; i < n; ++i) {
for (int j = 0; j < m; ++j) {
if (map[i].charAt(j) == 'S') {
x = i;
y = j;
}
}
}
Points point = new Points(x, y);//静态方法 调用非静态的内部类报错；
bfs(point);
}

private static void bfs(Points point) {
// TODO Auto-generated method stub
Queue<Points> queue = new LinkedList<Points>();
queue.add(point);
visit[point.getX()][point.getY()]=true;
while (!queue.isEmpty()) {
Points father = queue.poll();
int headx = father.getX();
int heady = father.getY();
for (int i = 0; i < dir.length; i++) {
int x = headx+dir[i][0];
int y = heady+dir[i][1];
Points son = new Points(x, y);
if ((-1 < x && x < n) && (-1 < y && y < m)) {
if (visit[x][y]==false) {
if (map[x].charAt(y) == '#') {
visit[x][y]=true;
continue;
}else if (map[x].charAt(y) == 'T') {
int count =1;
while (!(father.getX()==point.getX()&&father.getY()==point.getY())) {
father = father.getFathrpoint();
count++;
}
System.out.println(count);
return;
}else {
visit[x][y]=true;
son.setFathrpoint(father);
queue.add(son);
}
}
}
}
}
System.out.println("-1");
}

static class Points{
int x;
int y;
Points fathrpoint;
public Points getFathrpoint() {
return fathrpoint;
}
public void setFathrpoint(Points fathrpoint) {
this.fathrpoint = fathrpoint;
}
public int getX() {
return x;
}
public void setX(int x) {
this.x = x;
}
public int getY() {
return y;
}
public void setY(int y) {
this.y = y;
}
protected Points(int x,int y){
this.x=x;
this.y=y;
}
}
}