Robotti

input/code.cpp: In function 'void dfs(int, int, int)':
input/code.cpp:12:6: warning: infinite recursion detected [-Winfinite-recursion]
   12 | void dfs(int x, int y, int d) {
      |      ^~~
input/code.cpp:44:12: note: recursive call
   44 |         dfs(x+dx[nd], y+dy[nd], nd);
      |         ~~~^~~~~~~~~~~~~~~~~~~~~~~~
input/code.cpp:44:20: warning: 'nd' may be used uninitialized [-Wmaybe-uninitialized]
   44 |         dfs(x+dx[nd], y+dy[nd], nd);
      |               ~~~~~^
input/code.cpp:18:13: note: 'nd' was declared here
   18 |         int nd;
      |             ^~

#include<bits/stdc++.h>
using namespace std;

const int mxN=20;
int n, ans=0;
char grid[mxN][mxN];

//       D   R  U   L
int dx[4]{1, 0, -1, 0};
int dy[4]{0, 1, 0, -1};

void dfs(int x, int y, int d) {
	if(x<0 || x==n || y<0 || y==n) {
		cout << ans;
		exit(0);
	}
	ans++;
	int nd;
	if(grid[x][y]=='/') { // depending on the direction
		grid[x][y]='\\';
		if(d==1) { // we were going right, now we are going up
			nd=2;
		} else if(d==0) { // we are going down
			nd=3;
		} else if(d==2) { // we were going up
			nd=1;
		} else if(d==3) { // we were going to the left
			nd=0;
		}
	} else if(grid[x][y]=='\\') { // depending on the direction
		grid[x][y]='/';
		if(d==0) {
			nd=1;
		} else if(d==1) {
			nd=0;
		} else if(d==2) {
			nd=3;
		} else if(d==3) {
			nd=2;
		}
	} else { // do the same thing
		nd=d;
	}
	dfs(x+dx[nd], y+dy[nd], nd);
	return;
}

int main() {
	cin >> n;
	for(int i=0; i<n; i++) {
		for(int j=0; j<n; j++) {
			cin >> grid[i][j];
		}
	}
	dfs(0, 0, 0);
}

Test 1 (public)

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED