rbgraph.cpp

#include <iostream>

using namespace std;

const int NONE = 0;
const int RED = 1;
const int BLUE = 2;

int n;
int colors[5000] = {};
int mat[5000][5000] = {};
bool YES = true;

void ds(int k, int type);

int main(){

    cin >> n;
    char tmpc;

    for (int i = 1; i < n; i++)
        for (int j = i; j < n; j++){
            cin >> tmpc;
            if (tmpc == 'R')
                mat[i - 1][j] = RED;
            else
                mat[i - 1][j] = BLUE;
        }

    for (int i = 0; i < n; i++){
        ds(i, NONE);
        for (int j = 0; j < n; j++)
            colors[j] = NONE;
    }
    if (YES)
        cout << "YES" << endl;
    else
        cout << "NO" << endl;

    return 0;
}

void ds(int k, int type){
    if (colors[k] == NONE){
        colors[k] = type;
    }else{
        if (colors[k] != type && type != NONE){
            YES = false;
            return;
        }
    }
    for (int i = k + 1; i < n; i++){
        if (mat[k][i] == type || type == NONE)
            ds(i, mat[k][i]);
        if (!YES)
            break;
    }
}