没输出

#include<iostream>//广度优先搜索
#include<queue>
using namespace std;
struct cow//牛牛结构体 
{
	int num;//步数 
	int x;//坐标 
	int y; 
}; 
//变量和数组
int n, m, x, y;
int x2, y2;
int ax[4] = {0, 1, 0, 1};
int ay[4] = {1, 1, 0, 0};
char mg[400][400];//地图
bool flag[400][400];
bool tmp;
queue<cow> q;//牛牛 

void search(int x1,int y1){
	char ch = mg[x1][y1];
	for(int i = 0;i < n;i++){
		for(int j = 0;j < m;j++){
			if(mg[i][j] == ch  &&  i != x1  &&  j != y1){
				x2 = i;
				y2 = j;
			}
		}
	}
}

int main(){
	cin >> n >> m;
	
	cow n1,n2;
	for(int i = 0;i < n;i++){
		for(int j = 0;j < m;j++){
			cin >> mg[i][j];
			if(mg[i][j] == '@'){
				n1.x = i;
				n1.y = j;
			}
		}
	}
	flag[x][y] = true;
	
	n1.num = 0;
	
	q.push(n1);//1 初始状态入队
	//2 队列非空反复执行
	while(!q.empty()){
		
		n1 = q.front();//保留 

		
		//2-1 队头元素出队
		q.pop();//出队
				
		if(mg[n1.x][n1.y] == '='){
			cout << n1.num << endl;
			exit(0);
		}
			
		//2-2 拓展新状态，合法新状态入队
		for(int i = 0;i < 4;i++){
			tmp = false;
			n2.x = n1.x + ax[i];
			n2.y = n1.y + ay[i];
			n2.num = n1.num + 1;
			if(n2.x >= 0 && n2.x < n && n2.y >= 0 && n2.y < m && flag[n2.x][n2.y] == false){
				for(char j ='A';j<='Z';j++){
					if(mg[n2.x][n2.y] == j){
						search(n2.x,n2.y);
						tmp = true;
					}
				}
				if(tmp){
					flag[n2.x][n2.y] = true;
					n2.x = x2;
					n2.y = y2;
				}
				flag[n2.x][n2.y] = true;
				q.push(n2);
			}
		}
	}
	return 0;
}