USACO 2.4 The Tamworth Two

The problem can be solved using simple search. The only catch seems that we need properly encode the global state such that we don’t end up visit two exact same state twice, so we can bail out in cases where farmer and cows would never meet.
The visited state can be encoded using a six dimensional array, with dimensions as farmers locations (x, y), direction, and cows locations (x, y) and direction.

#include <algorithm>
#include <vector>
#include <iostream>
#include <fstream>
#include <utility>
#include <unordered_map>
#include <set>
#include <stack>

using namespace std;

bool visited[10][10][4][10][10][4] = {false};
vector<vector<char>> grid(10, vector<char>(10, ' '));
// Encoding of directions: 0, 1, 2, 3 for north, east, south, west.
int fd = 0, cd = 0;
typedef struct state {
    int x; int y; int d;
    state() : x(0), y(0), d(0) {}
} tState;
tState fs, cs;

void move(tState &s) {
    if (s.d == 0) {
        --s.y;
        if (s.y < 0 || grid[s.y][s.x] == '*') {
            ++s.y;
            s.d = 1;
        }
    } else if (s.d == 1) {
        ++s.x;
        if (s.x > 9 || grid[s.y][s.x] == '*') {
            --s.x;
            s.d = 2;
        }
    } else if (s.d == 2) {
        ++s.y;
        if (s.y > 9 || grid[s.y][s.x] == '*') {
            --s.y;
            s.d = 3;
        }
    } else if (s.d == 3) {
        --s.x;
        if (s.x < 0 || grid[s.y][s.x] == '*') {
            ++s.x;
            s.d = 0;
        }
    } else {
        cout << "Invalid State!!" << endl;
    }
}

int main() {
    ifstream fin("ttwo.in");
    ofstream fout("ttwo.out");
    
    char c;
    for (int i = 0; i < 10; ++i) {
        for (int j = 0; j < 10; ++j) {
            fin >> c;
            grid[i][j] = c;
            if (c == 'F') {
                fs.x = j; fs.y = i;
            }
            if (c == 'C') {
                cs.x = j; cs.y = i;
            }
            cout << grid[i][j] << " ";
        }
        cout << endl;
    }
    
    visited[fs.x][fs.y][fs.d][cs.x][cs.y][cs.d] = true;
    int res = 0;
    while (true) {
        ++res;
        move(fs);
        move(cs);
        if (visited[fs.x][fs.y][fs.d][cs.x][cs.y][cs.d]) {
            res = 0; break;
        }
        
        if (fs.x == cs.x && fs.y == cs.y) {
            break;
        }
        
        visited[fs.x][fs.y][fs.d][cs.x][cs.y][cs.d] = true;
    }
    
    fout << res << endl;
    cout << res << endl;
}