<p>You are given an integer <code>n</code>, the number of nodes in a directed graph where the nodes are labeled from <code>0</code> to <code>n - 1</code>. Each edge is red or blue in this graph, and there could be self-edges and parallel edges.</p>

<p>You are given two arrays <code>redEdges</code> and <code>blueEdges</code> where:</p>

<ul>
	<li><code>redEdges[i] = [a<sub>i</sub>, b<sub>i</sub>]</code> indicates that there is a directed red edge from node <code>a<sub>i</sub></code> to node <code>b<sub>i</sub></code> in the graph, and</li>
	<li><code>blueEdges[j] = [u<sub>j</sub>, v<sub>j</sub>]</code> indicates that there is a directed blue edge from node <code>u<sub>j</sub></code> to node <code>v<sub>j</sub></code> in the graph.</li>
</ul>

<p>Return an array <code>answer</code> of length <code>n</code>, where each <code>answer[x]</code> is the length of the shortest path from node <code>0</code> to node <code>x</code> such that the edge colors alternate along the path, or <code>-1</code> if such a path does not exist.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> n = 3, redEdges = [[0,1],[1,2]], blueEdges = []
<strong>Output:</strong> [0,1,-1]
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> n = 3, redEdges = [[0,1]], blueEdges = [[2,1]]
<strong>Output:</strong> [0,1,-1]
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= n &lt;= 100</code></li>
	<li><code>0 &lt;= redEdges.length,&nbsp;blueEdges.length &lt;= 400</code></li>
	<li><code>redEdges[i].length == blueEdges[j].length == 2</code></li>
	<li><code>0 &lt;= a<sub>i</sub>, b<sub>i</sub>, u<sub>j</sub>, v<sub>j</sub> &lt; n</code></li>
</ul>

class Solution {
public:
    vector<int> shortestAlternatingPaths(int n, vector<vector<int>>& redEdges, vector<vector<int>>& blueEdges) {
        //two graphs of red and blue edges, bfs
        vector<int>gr[n], gb[n];
        for(auto& e:redEdges) gr[e[0]].push_back(e[1]);
        for(auto& e:blueEdges) gb[e[0]].push_back(e[1]);
        vector<int>rdist(n,1e9), bdist(n,1e9); rdist[0]=0; bdist[0]=0;
        int rvis[n], bvis[n]; memset(rvis,0,sizeof(rvis)); memset(bvis,0,sizeof(bvis)); rvis[0]=1; bvis[0]=1;
        queue<array<int,2>>q; q.push({0,1}); q.push({0,2});
        while(!q.empty()){
            array<int,2>v=q.front(); q.pop();
            if(v[1]==1){
                for(int ch:gb[v[0]]){
                    if(bvis[ch]) continue;
                    bvis[ch]=1;
                    bdist[ch]=rdist[v[0]]+1;
                    q.push({ch,2});
                }
            }
            else{
                for(int ch:gr[v[0]]){
                    if(rvis[ch]) continue;
                    rvis[ch]=1;
                    rdist[ch]=bdist[v[0]]+1;
                    q.push({ch,1});
                }
            }
        }
        vector<int>ans(n);
        for(int i=0;i<n;++i){
            ans[i]=min(bdist[i],rdist[i]);
            if(ans[i]==1e9) ans[i]=-1;
        }
        return ans;
    }
};
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