Language: C++

#include <algorithm>
#include <bitset>
#include <cassert>
#include <cctype>
#include <cfloat>
#include <climits>
#include <cmath>
#include <cstdio>
#include <deque>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <unordered_set>
#include <vector>
using namespace std;
typedef long double ld;
typedef long long int ll;
typedef unsigned long long int ull;
typedef vector<int> vi;
typedef vector<char> vc;
typedef vector<bool> vb;
typedef vector<double> vd;
typedef vector<string> vs;
typedef vector<ll> vll;
typedef vector<pair<int, int>> vpii;
typedef vector<pair<ll, ll>> vpll;
typedef vector<vi> vvi;
typedef vector<vvi> vvvi;
typedef vector<vc> vvc;
typedef vector<vs> vvs;
typedef vector<vll> vvll;
typedef map<int, int> mii;
typedef set<int> si;
#define rep(i, n) for (ll i = 0; i < (n); ++i)
#define rrep(i, n) for (int i = 1; i <= (n); ++i)
#define arep(i, v) for (auto i : v)
#define irep(it, stl) for (auto it = stl.begin(); it != stl.end(); it++)
#define drep(i, n) for (int i = (n)-1; i >= 0; --i)
#define fin(ans) cout << (ans) << '\n'
#define STLL(s) strtoll(s.c_str(), NULL, 10)
#define mp(p, q) make_pair(p, q)
#define pb(n) push_back(n)
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define Sort(a) sort(a.begin(), a.end())
#define Rort(a) sort(a.rbegin(), a.rend())
#define MATHPI acos(-1)
#define fi first
#define se second
#include <atcoder/all>
using namespace atcoder;
constexpr int dx[8] = {1, 0, -1, 0, 1, -1, -1, 1};
constexpr int dy[8] = {0, 1, 0, -1, 1, 1, -1, -1};
template <class T>
inline bool chmax(T &a, T b) {
    if (a < b) {
        a = b;
        return 1;
    }
    return 0;
}
template <class T>
inline bool chmin(T &a, T b) {
    if (a > b) {
        a = b;
        return 1;
    }
    return 0;
}
template <class T>
inline void dump(T &v) {
    irep(i, v) { cout << (*i) << ((i == --v.end()) ? '\n' : ' '); }
}
template <class T, class U>
inline void dump(map<T, U> &v) {
    irep(i, v) { cout << i->first << " " << i->second << '\n'; }
}
inline string getline() {
    string s;
    getline(cin, s);
    return s;
}
inline void yn(const bool b) { b ? fin("yes") : fin("no"); }
inline void Yn(const bool b) { b ? fin("Yes") : fin("No"); }
inline void YN(const bool b) { b ? fin("YES") : fin("NO"); }
struct io {
    io() {
        ios::sync_with_stdio(false);
        cin.tie(0);
    }
};
const int INF = INT_MAX;
constexpr ll LLINF = 1LL << 61;
constexpr ll MOD = 1000000007;
constexpr ld EPS = 1e-11;

/* --------------------   ここまでテンプレ   -------------------- */

int main() {
    int n, m;
    cin >> n >> m;
    mf_graph<int> graph(2 * n * m + 2);
    vs v(n);
    rep(i, n) cin >> v[i];
    rep(i, n) {
        rep(j, m) {
            if (v[i][j] == '#') continue;
            for (int k = 0; k < 4; k++) {
                int nx = j + dx[k];
                int ny = i + dy[k];
                if (nx >= m || ny >= n || nx < 0 || ny < 0) continue;
                if (v[ny][nx] == '#') continue;
                graph.add_edge(i * m + j, n * m + ny * m + nx, 1);
            }
            graph.add_edge(2 * n * m, i * m + j, 1);
            graph.add_edge(n * m + i * m + j, 2 * n * m + 1, 1);
        }
    }
    int cap = graph.flow(2 * n * m, 2 * n * m + 1);
    auto ed = graph.edges();
    rep(i, ed.size()) {
        if (ed[i].from >= 2 * n * m || ed[i].to >= 2 * n * m) continue;
        if (!ed[i].flow) continue;
        ed[i].from %= n * m;
        ed[i].to %= n * m;
        // cout << ed[i].from << " " << ed[i].to << " " << ed[i].flow << endl;
        int from_x = ed[i].from%m;
        int from_y = ed[i].from/m;
        int to_x = ed[i].to%m;
        int to_y = ed[i].to/m;
        if(from_x>to_x)swap(from_x,to_x);
        if(from_y>to_y)swap(from_y,to_y);
        if(from_x == to_x){
            // 縦
            v[from_y][from_x] = 'v';
            v[to_y][to_x] = '^';
        } else {
            // 横
            v[from_y][from_x] = '>';
            v[to_y][to_x] = '<';
        }
    }
    rep(i,n)fin(v[i]);
}


Compiler output:
a.cc:56:10: fatal error: atcoder/all: No such file or directory
   56 | #include <atcoder/all>
      |          ^~~~~~~~~~~~~
compilation terminated.