宣传一下$\Huge\color{green}{春季每日一题题解}$

其实，我当时考虑多了，并不是什么图论……（呜呜），DFS也不会TLE……

#include<bits/stdc++.h>
using namespace std;
int dx[] = {-1, 0, 1, 0}, dy[] = {0, 1, 0, -1};
char Map[1010][1010];
int n, m, ans;
void dfs(int f, int x, int y, int a) {
    ans = max(ans, a);
    int fx = 0;
    if(Map[x][y] == '/') fx = f ^ 1;
    else fx = f ^ 3;
    int xx = x + dx[fx], yy = y + dy[fx];
    if(xx >= 1 && xx <= n && yy >= 1 && yy <= m) dfs(fx, xx, yy, a + 1);
}

int main(){
    scanf("%d%d", &n, &m);
    for(int i = 1; i <= n; i++) cin >> (Map[i] + 1);
    for(int i = 1; i <= m; i++) dfs(2, 1, i, 1), dfs(0, n, i, 1);
    for(int i = 1; i <= n; i++) dfs(1, i, 1, 1), dfs(3, i, m, 1);
    printf("%d", ans);
    return 0;
}