Is Graph Bipartite?

[huimeich]

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 i will be in graph[j].

[huimeich]

def isBipartite(self, graph: List[List[int]]) -> bool:
    g = [-1] * len(graph)
    stack = []
    for curr in range(len(graph)):
        if g[curr] > -1:
            continue
        stack.append(curr)
        g[curr] = 0
        while stack:
            node = stack.pop()
            for nb in graph[node]:
                if g[nb] >= 0:
                    if g[node] == g[nb]:
                        return False
                else:
                    g[nb] = 1-g[node]
                    stack.append(nb)
    return True