Language: C++

#include <bits/stdc++.h>
#include <unistd.h>
#include <sys/time.h>
#include <stdlib.h>
#include <atcoder/maxflow>

using namespace std;
using namespace atcoder;



typedef long long ll;
typedef pair<ll, ll> P;
typedef pair<P, ll> T;
typedef pair<long double , ll> Ps;
typedef pair<ll, bool> Pb;
typedef pair<ll, vector<ll>> Pd;

const ll INF = 1e18;
const ll fact_table = 3200008;
long double Pi = 3.1415926535897932384626;

priority_queue <ll> pql;
priority_queue <P> pqp;
priority_queue <P> bag;
//big priority queue
priority_queue <ll, vector<ll>, greater<ll> > pqls;
priority_queue <P, vector<P>, greater<P> > pqps;
//small priority queue
//top pop

ll dx[8] = {1, 0, -1, 0, 1, 1, -1, -1};
ll dy[8] = {0, 1, 0, -1, 1, -1, -1, 1};
//↓,→,↑,←


#define endl "\n"
#ifdef ENJAPMA
#undef endl
#endif

#define p(x) cout<<x<<endl;
#define el cout<<endl;
#define pe(x) cout<<x<<" ";
#define ps(x) cout<<fixed<<setprecision(25)<<x<<endl;
#define pu(x) cout<<(x);
#define pb push_back
#define lb lower_bound
#define ub upper_bound
#define CLEAR(a) a = decltype(a)();
#define pc(x) cout << x << ",";
#define rep(i, n) for (ll i = 0; i < (n); i ++)

typedef vector<ll> vec;
typedef vector<vector<ll>> mat;

const ll mod = 998244353ll;
// const ll mod = 1000000007ll;

ll mypow(ll a, ll b, ll m = mod) {ll x = 1; while (b) {while (!(b & 1)) {(a *= a) %= m; b >>= 1;}(x *= a) %= m; b--;} return x;}
vec readvec(ll read) { vec res(read); for (int i = 0; i < read; i++) { cin >> res[i]; } return res;}
void YES(bool cond) { if (cond) { p("YES");} else { p("NO");} return;}
void Yes(bool cond) { if (cond) { p("Yes");} else { p("No");} return;}
void line() { p("--------------------"); return;}

/*
ll fact[fact_table + 5], rfact[fact_table + 5];

void c3_init() {
    fact[0] = rfact[0] = 1;
    for (ll i = 1; i <= fact_table; i++) {
        fact[i] = (fact[i - 1] * i) % mod;
    }
    rfact[fact_table] = mypow(fact[fact_table], mod - 2, mod);
    for (ll i = fact_table; i >= 1; i--) {
        rfact[i - 1] = rfact[i] * i;
        rfact[i - 1] %= mod;
    }
    return;
}
ll c3(ll n, ll r) {
    return (((fact[n] * rfact[r]) % mod ) * rfact[n - r]) % mod;
}
*/



struct Timer {
    int64_t start; const int64_t CYCLES_PER_SEC = 2800000000;
    Timer() { reset(); }
    void reset() { start = getCycle(); }
    inline double get() { return (double)(getCycle() - start) / CYCLES_PER_SEC; }
    inline int64_t getCycle() {
        uint32_t low, high; __asm__ volatile ("rdtsc" : "=a" (low), "=d" (high));
        return ((int64_t)low) | ((int64_t)high << 32);
    }
};

bool multicase = false;
string s[105];

ll n, m;

void ansPrint(int fromid, int toid){
    int fx = fromid / m, fy = fromid % m;
    int tx = toid / m, ty = toid % m;
    if (fx == tx) {
        s[fx][min(fy, ty)] = '>';
        s[fx][max(fy, ty)] = '<';
    } else {
        s[min(fx, tx)][fy] = 'v';
        s[max(fx, tx)][fy] = '^';
    }
}

void solve() {
    cin >> n >> m;
    mf_graph<ll> graph(n * m + 2);
    ll maxi = n * m;
    for (int i = 0; i < n; i++) {
        cin >> s[i];
    }
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < m; j++) {
            if (s[i][j] == '#') continue;
            int id = i * m + j;
            bool flag = ((i + j) % 2 == 1);
            if (flag) {
                graph.add_edge(maxi, id, 1);
                for (int k = 0; k < 4; k++) {
                    ll nx = i + dx[k], ny = j + dy[k];
                    if (nx < 0 || ny < 0 || n <= nx || m <= ny) continue;
                    if (s[nx][ny] == '#') continue;
                    int nid = nx * m + ny;
                    graph.add_edge(id, nid, 1);
                }
            } else {
                graph.add_edge(id, maxi + 1, 1);
            }
        }
    }
    ll res = graph.flow(maxi, maxi + 1);
    p(res);

    auto E = graph.edges();
    for (auto edge : E) {
        int fromid = edge.from, toid = edge.to;
        if (fromid == maxi || toid == maxi + 1) continue;
        if (edge.flow == 0) continue;
        ansPrint(fromid, toid);
    }

    for(int i=0;i<n;i++){
        p(s[i]);
    }
    return;
}

int main() {
    // init();
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    ll q, testcase = 1;
    if (multicase) {
        cin >> q;
    } else {
        q = 1;
    }
    while (q--) {
        // pu("Case ");pu("#");pu(testcase);pu(": ");
        solve();
        testcase++;
    }

    // solve();
    return 0;
}






Compiler output:
a.cc:5:10: fatal error: atcoder/maxflow: No such file or directory
    5 | #include <atcoder/maxflow>
      |          ^~~~~~~~~~~~~~~~~
compilation terminated.