Language: C++

/**
 *	author: nok0
 *	created: 2020.09.08 08:04:36
**/
#include <bits/stdc++.h>
using namespace std;
#include <atcoder/all>
using namespace atcoder;
#pragma region Macros
#define ll long long
#define ld long double
#define FOR(i,l,r) for(int i=(l);i<(r);++i)
#define REP(i,n) FOR(i,0,n)
#define REPS(i,n) FOR(i,1,n+1)
#define RFOR(i,l,r) for(int i=(l);i>=(r);--i)
#define RREP(i,n) RFOR(i,n-1,0)
#define RREPS(i,n) RFOR(i,n,1)
#define pb push_back
#define eb emplace_back
#define SZ(x) ((int)(x).size())
#define all(x) (x).begin(),(x).end()
#define rall(x) (x).rbegin(),(x).rend()
template<class T = int> using V = vector<T>;
template<class T = int> using VV = V<V<T>>;
using P = pair<int, int>;
#define VEC(type, name, size)\
	V<type> name(size);\
	IN(name)
#define VVEC(type, name, h, w)\
	VV<type> name(h, V<type>(w));\
	IN(name)
#define INT(...)\
	int __VA_ARGS__;\
	IN(__VA_ARGS__)
#define LL(...)\
	ll __VA_ARGS__;\
	IN(__VA_ARGS__)
#define STR(...)\
	string __VA_ARGS__;\
	IN(__VA_ARGS__)
#define CHAR(...)\
	char __VA_ARGS__;\
	IN(__VA_ARGS__)
#define DOUBLE(...)\
	DOUBLE __VA_ARGS__;\
	IN(__VA_ARGS__)
#define LD(...)\
	LD __VA_ARGS__;\
	IN(__VA_ARGS__)
template <class T> void scan(T a) { cin >> a; }
void scan(int &a) { cin >> a; }
void scan(long long &a) { cin >> a; }
void scan(char &a) { cin >> a; }
void scan(double &a) { cin >> a; }
void scan(long double &a) { cin >> a; }
void scan(char a[]) { scanf("%s", a); }
void scan(string &a) { cin >> a; }
template <class T> void scan(V<T> &);
template <class T, class L> void scan(pair<T, L> &);
template <class T> void scan(V<T> &a) { for(auto &i : a) scan(i); }
template <class T, class L> void scan(pair<T, L> &p){ scan(p.first); scan(p.second); }
template <class T> void scan(T &a) { cin >> a; }
void IN() {}
template <class Head, class... Tail> void IN(Head &head, Tail &... tail) { scan(head); IN(tail...); }
template <class T> inline void print(T x){ cout << x << '\n';}
template <typename T1, typename T2>
istream &operator>>(istream &is, pair<T1, T2> &p){
	is >> p.first >> p.second;
	return is;
}
template <typename T1, typename T2>
ostream &operator<<(ostream &os, const pair<T1, T2> &p){
	os << p.first << " " << p.second;
	return os;
}
template <class T>
ostream &operator<<(ostream &os, const V<T> &v){
	REP(i, SZ(v)){
		if(i) os << " ";
		os << v[i];
	}
	return os;
}
//debug
template <typename T>
void view(const V<T> &v){
	cerr << "{ ";
	for(const auto &e : v){
		cerr << e << ", ";
	}
	cerr << "\b\b }";
}
template <typename T>
void view(const VV<T> &vv){
	cerr << "{\n";
	for(const auto &v : vv){
		cerr << "\t";
		view(v);
		cerr << "\n";
	}
	cerr << "}";
}
template <typename T, typename U>
void view(const V<pair<T, U>> &v){
	cerr << "{\n";
	for(const auto &c : v) cerr << "\t(" << c.first << ", " << c.second << ")\n";
	cerr << "}";
}
template <typename T, typename U>
void view(const map<T, U> &m){
	cerr << "{\n";
	for(auto &t : m) cerr << "\t[" << t.first << "] : " << t.second << "\n";
	cerr << "}";
}
template <typename T, typename U>
void view(const pair<T, U> &p){ cerr << "(" << p.first << ", " << p.second << ")";}
template <typename T>
void view(const set<T> &s) {
	cerr << "{ ";
	for(auto &t : s) {
		view(t);
		cerr << ", ";
	}
	cerr << "\b\b }";
}
template <typename T>
void view(T e) { cerr << e;}
#ifdef LOCAL
void debug_out() {}
template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
	view(H);
	cerr << ", ";
	debug_out(T...);
}
#define debug(...)                                           \
	do{                                                     \
		cerr << __LINE__ << " [" << #__VA_ARGS__ << "] : ["; \
		debug_out(__VA_ARGS__);                              \
		cerr << "\b\b]\n";                                   \
	} while(0)
#else
#define debug(...) (void(0))
#endif
template <class T> V<T> press(V<T> &x){ 
	V<T> res = x;
	sort(all(res));
	res.erase(unique(all(res)), res.end());
	REP(i, SZ(x)){
		x[i] = lower_bound(all(res), x[i]) - res.begin();
	}
	return res;
}
template<class T> inline bool chmin(T& a, T b) {if (a > b) {a = b; return true; }return false; }
template<class T> inline bool chmax(T& a, T b) {if (a < b) {a = b; return true; }return false; }
inline void Yes(bool b = true) {cout << (b ? "Yes" : "No") << '\n';}
inline void YES(bool b = true) {cout << (b ? "YES" : "NO") << '\n';}
inline void err(bool b = true) {if(b) {cout << -1 << '\n'; exit(0);}}
template<class T> inline void fin(bool b = true, T e = 0) {if(b) {cout << e << '\n'; exit(0);}}
template<class T> T divup(T x, T y) {return (x+(y-1))/y;}
template <typename T> T pow(T a, long long n, T e = 1) {T ret = e; while (n) {if (n & 1) ret *= a; a *= a; n >>= 1; } return ret; }
const ll INF = 1e18;
#pragma endregion

int dx[2] = {1, 0}, dy[2] = {0, 1};

int main(){
	INT(n, m);
	VVEC(char, a, n, m);
	mf_graph<int> mf(n * m + 2);
	int s = n * m, t = n * m + 1,
	REP(i, n) REP(j, m){
		if(a[i][j] == '#') continue;
		int x = i * m + j;
		if(x % 2) mf.add_edge(s, x, 1);
		else mf.add_edge(x, t, 1);
		REP(k, 2){
			int nx = i + dx[k], ny = j + dy[k];
			if(nx >= n or ny >= m or a[nx][ny] == '#') continue;
			int y = nx * m + ny;
			if(x % 2) mf.add_edge(x, y, 1);
			else mf.add_edge(y, x, 1);
			debug(x, y);
		}
	}
	print(mf.flow(s, t));
	for(auto e : mf.edges()){
		if(e.from == s or e.to == t or !e.flow) continue;
		int x0 = e.from / m, y0 = e.from % m, x1 = e.to / m, y1 = e.to % m;
		debug(x0,y0,x1,y1,e.flow);
		if(x0 == x1){
			if(y0 < y1) a[x0][y0] = '>', a[x1][y1] = '<';
			else a[x0][y0] = '<', a[x1][y1] = '>';
		}
		else{
			if(x0 < x1) a[x0][y0] = 'v', a[x1][y1] = '^';
			else a[x0][y0] = '^', a[x1][y1] = 'v';
		}
	}
	REP(i, n){
		REP(j, m)cout << a[i][j];
		cout << endl;
	}
}

Compiler output:
a.cc:7:10: fatal error: atcoder/all: No such file or directory
    7 | #include <atcoder/all>
      |          ^~~~~~~~~~~~~
compilation terminated.