Leetcode|并查集|785. 判断二分图

class UnionFind {
public:
    int count;
    vector<int> parent, size;

    UnionFind(int n) {
        count = n;
        parent.resize(n);
        size.resize(n);
        for (int i = 0; i < n; i++) {
            parent[i] = i;
            size[i] = 1;
        }
    }

    void unite(int a, int b) {
        int rootA = find_root(a);
        int rootB = find_root(b);
        if (rootA == rootB) return;
        if (size[rootA] < size[rootB]) {
            parent[rootA] = rootB;
            size[rootB] += size[rootA];
        } else {
            parent[rootB] = rootA;
            size[rootA] += size[rootB];
        }
        count--;
    }

    int find_root(int node) {
        while (parent[node] != node) {
            parent[node] = parent[parent[node]];
            node = parent[node];
        }
        return node;
    }

    bool connected(int a, int b) {
        int rootA = find_root(a);
        int rootB = find_root(b);
        return rootA == rootB;
    }
};

class Solution {
public:
    bool isBipartite(vector<vector<int>>& graph) {
        int size = graph.size();
        UnionFind uf(size);
        // 1.遍历图中每个顶点
        for (int i = 0; i < size; i++) {
            // 遇到孤立点，不影响二分图性质，直接跳过
            if (graph[i].empty()) continue;
            int v = graph[i][0];
            // 2.遍历与顶点相连的所有邻接点
            for (int j = 1; j < graph[i].size(); j++) {
                // 若顶点与邻接点被分同一类，则不满足二分图性质
                if (uf.connected(i, graph[i][j])) return false;
                // 将每个邻接点聚类
                uf.unite(v, graph[i][j]);
                v = graph[i][j];
            }
        }
        return true;
    }
};