c_cpp 684.冗余连接（第1个）.cpp

Posted 2021-05-14

public class Solution {
    public int[] findRedundantConnection(int[][] edges) {
        if (edges == null || edges.length < 1 || edges[0].length < 1) return new int[0];
        int n = edges.length + 1;
        UnionFind uf = new UnionFind(2010);
        for (int[] e : edges) {
            uf.make_set(e[0]);
            uf.make_set(e[1]);
        }
        for (int[] e : edges) {
            if (uf.find(e[0]) != uf.find(e[1])) {
                uf.union(e[0], e[1]);
            } else {
                return e;
            }
        }
        return new int[0];
    }
}
class UnionFind {
    private int[] parent;
    private int[] size;
    private int n, count;
    
    public UnionFind (int n) {
        this.n = n;
        this.count = n;
        parent = new int[n];
        size = new int[n];
    }
    
    public void make_set(int x) {
        parent[x] = x;
        size[x] = 1;
    }
    
    public int find(int x) {
        // if (parent[x] != x) {
        //     parent[x] = find(parent[x]);
        // }
        while (parent[x] != x) {
            parent[x] = parent[parent[x]];
            x = parent[x];
        }
        
        return x;
    }
    
    public void union(int x, int y) {
        int parentX = find(x);
        int parentY = find(y);
        if (parentX != parentY) {
            if (size[parentX] > size[parentY]) {
                parent[parentY] = parentX;
                size[parentX] += size[parentY];
            } else {
                parent[parentX] = parentY;
                size[parentY] += size[parentX];
            }
            count--;
        } 
    }
    
    public int getCount() {
        return count;
    }
}

class Solution {
public:
    vector<int> findRedundantConnection(vector<vector<int>>& edges) {
        map<int, int> parent;
        for (auto e : edges) {
            if (parent.find(e[1]) != parent.end()) {
                return e; 
            }
            if (parent.find(e[0]) != parent.end()) {
                if (parent[e[0]] == e[1])
                    return e;
            }
            parent[e[1]] = e[0];
        } 
        set<int> root;
        for (auto e : edges) {
            if (root.find(e[1]) != root.end())
                return e;
            root.insert(e[0]);
        }
        return edges.back();
    }
};