LeetCode [785] Is Graph Bipartite?

Given an undirected graph, return true if and only if it is bipartite.

Recall that a graph is bipartite if we can split it's set of nodes into two independent subsets A and B such that every edge in the graph has one node in A and another node in B.

The graph is given in the following form: graph[i] is a list of indexes j for which the edge between nodes i and j exists.  Each node is an integer between 0 and graph.length - 1.  There are no self edges or parallel edges: graph[i] does not contain i, and it doesn't contain any element twice.

Example 1:
Input: [[1,3], [0,2], [1,3], [0,2]]
Output: true
Explanation: 
The graph looks like this:
0----1
|    |
|    |
3----2
We can divide the vertices into two groups: {0, 2} and {1, 3}.

Example 2:
Input: [[1,2,3], [0,2], [0,1,3], [0,2]]
Output: false
Explanation: 
The graph looks like this:
0----1
| \  |
|  \ |
3----2
We cannot find a way to divide the set of nodes into two independent subsets.

Note:

• graph will have length in range [1, 100].
• graph[i] will contain integers in range [0, graph.length - 1].
• graph[i] will not contain i or duplicate values.
• The graph is undirected: if any element j is in graph[i], then iwill be in graph[j].

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//try color sets with two colors //if nodes on the same edge end up with same color then the graph is not bipartite class Solution { public: bool isBipartite(vector<vector<int>>& graph) { int sz = graph.size(); vector<int> colors(sz, 0);//0(uncolored) 1(blue) -1(red) for(int i=0; i<sz; ++i) { //node i is note colored yet, chose any color if(colors[i]==0 && !valid(i, 1, colors, graph)) return false; } return true; } bool valid(int i, int color, vector<int>& colors, vector<vector<int>>& graph) { colors[i] = color; for(auto n:graph[i]) { if(colors[n]==color) return false;//nodes on the same edge have same color, conflict! if(colors[n]==0 && !valid(n, -color, colors, graph)) return false; } return true; } };