UVa 10004 - Bicoloring

// Accepted

#include<bits/stdc++.h>
using namespace std;

const int high = 500;

vector<int>adj[high];
int color[high];
bool bicolorable = true;

void adj_clear()
{
    for(int i=0; i<high; i++) adj[i].clear();
}

void BFS(int s)
{
    queue<int>Q;

    color[s] = 0;

    Q.push(s);

    while(!Q.empty())
    {
        int u = Q.front();
        Q.pop();

        for(int i=0; i<adj[u].size(); i++)
        {
            int v = adj[u][i];

            if(!color[v])
            {
                Q.push(v);
                color[v] = 1 + color[u]; // Just increase one from its parent node to make difference between two nodes.
            }

            else if(color[u] == color[v])
            {
                bicolorable = false;
                break;
            }
        }

        if(!bicolorable) break;
    }
}

int main()
{
    //freopen("in.txt" , "r" , stdin);
    ios_base::sync_with_stdio(false);

    int i , n , l , u , v;
    while(cin >> n >> l)
    {
        if(!n) break;

        bicolorable=true;
        memset(color , 0 , sizeof color);
        adj_clear();

        for(i=0; i<l; i++)
        {
            cin >> u >> v;
            adj[u].push_back(v);
            adj[v].push_back(u);
        }

        for(i=0; i<n; i++)
        {
            BFS(i);

            if(!bicolorable) break;
        }

        if(bicolorable) cout << "BICOLORABLE.\n";
        else cout << "NOT BICOLORABLE.\n";
    }

    return 0;
}