小菜鸡想用“右手原则”做

我想用传说中的“右手原则”过，可是TLE60分。其他的3、4毫秒就过了，但有四个竟然TLE？根据题目，终点不可能在中间，所以应该右手原则能过。不知是右手原则不对，是我代码编错了？

#include <iostream>
#include <vector>
#include <string>
const int dx[] = {-1, 0, 1, 0};
const int dy[] = {0, 1, 0, -1};
bool isValid(int x, int y, int n, int m) {
    return x >= 0 && x < n && y >= 0 && y < m;
}
bool solveMaze(std::vector<std::string>& maze, int n, int m) {
    int dir = 1;
    int x = 0, y = 0;
    while (true) {
        if (x == n - 1 && y == m - 1) {
            return true;
        }
        int right = (dir + 1) % 4;
        int nx = x + dx[right];
        int ny = y + dy[right];
        if (isValid(nx, ny, n, m) && maze[nx][ny] != '#') {
            x = nx;
            y = ny;
            dir = right;
        } else {
            nx = x + dx[dir];
            ny = y + dy[dir];
            if (isValid(nx, ny, n, m) && maze[nx][ny] != '#') {
                x = nx;
                y = ny;
            } else {
                dir = (dir + 3) % 4;
            }
        }
    }
    return false;
}
int main() {
    int n, m;
    std::cin >> n >> m;
    std::vector<std::string> maze(n);
    for (int i = 0; i < n; ++i) {
        std::cin >> maze[i];
    }
    if (solveMaze(maze, n, m)) {
        std::cout << "Yes" << std::endl;
    } else {
        std::cout << "No" << std::endl;
    }
    return 0;
}