785. Is Graph Bipartite? [Medium]

判断是否为二部图，本质是无向图的相邻节点涂色必须不同 

/**
 * 图的dfs
 * colored数组中，1和-1代表两个颜色
 * Runtime: 0 ms, faster than 100.00% 
 * Memory Usage: 39 MB, less than 97.60%
 */
class Solution {
    public boolean isBipartite(int[][] graph) {
        Integer[] colored = new Integer[graph.length];
        for (int i = 0; i < colored.length; i++) {
            if (colored[i] == null && !helper(graph, colored, i, 1)) { // 需要所有顶点都涂色，所以如果有没涂色的顶点，从它为根开始dfs涂色
                return false;
            }
        }
        return true;
    }
    private boolean helper(int[][] graph, Integer[] colored, int i, int color) {
        if (colored[i] == null) {
            colored[i] = color;
            for (int next : graph[i]) {
                if (!helper(graph, colored, next, -color)) {
                    return false;
                }
            }
        } else { // 已经涂过色，涂色不可改，比较涂色颜色是否符合要求
            if (colored[i] != color) {
                return false;
            }
        }
        return true;
    }
}

标签：785,Medium,return,colored,int,graph,color,涂色,Bipartite
来源： https://blog.csdn.net/Squirrelmi/article/details/116886424