Красно-синий граф

#include <iostream>
#include <bits/stdc++.h>
//#pragma GCC optimize("O3")
//#pragma GCC optimize("unroll-loops")

#define mp make_pair
#define pb push_back
#define eb emplace_back
#define x first
#define y second
//#define sz(x) (int)x.size()
#define all(x) begin(x), end(x)
#define rall(x) rbegin(x), rend(x)
#define FOR(i,a,b) for (int i = (a); i < (b); i++)
#define RFOR(i,b,a) for (int i = (b) - 1; i >= (a); i--)

using namespace std;

typedef unsigned long long ull;
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pi;
typedef pair<ld, ld> pld;
typedef pair<ll, ll> pl;
typedef vector<int> veci;
typedef vector<bool> vecb;
typedef vector<vector<int>> vvi;
typedef vector<vector<bool>> vvb;

const int INF_I = 1e9;
const ll INF_LL = 1e18;
const int MOD = 1000000007;
const double eps = 1e-6;

vector<vector<short>> g;
vector<char> c;
int n;

bool dfs(int v){
    if (v >= n)
        while(1){}
    c[v] = 1;
    for (int i : g[v]){
        if (c[i] == 0) {
            if (dfs(i))
                return true;
        }
        else if (c[i] == 1)
            return true;
    }
    c[v] = 2;
    return false;
}

int main() {

    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);

    cin >> n;
    g.assign(n, vector<short>());
    c.assign(n, 0);
    for (int i = 0; i < n-1; i++){
        for (int j = 0; j < n-i-1; j++){
            char ch;
            cin >> ch;
            if (ch == 'B')
                g[i].eb(i+j+1);
            else
                g[i+j+1].eb(i);
        }
    }

    for (int i = 0; i < n; i++)
        if (c[i] == 0 && dfs(i)) {
            cout << "NO\n";
            return 0;
        }
    cout << "YES\n";

    return 0;
}