图论第7天

今天去打了会羽毛球。最近还是有点累啊，今天尽量效率

1971. 寻找图中是否存在路径

第一步是先整init

第二步先把该关联的关联

第三步判断是否有路

class Solution {
private:
    int nMax = 200005;
    vector<int>father = vector<int>(nMax,0);
    void init(int num){
        for(int i = 0;i < num;i++){father[i] = i;
        }
    }
    int find(int x){
        return x == father[x] ? x : father[x] = find(father[x]);
    }
    bool isSame(int a,int b){
        a = find(a);
        b = find(b);
        return a == b;
    }
    void join(int a ,int b){
        a = find(a);
        b = find(b);
        if(a == b)return;
        father[b] = a;
    }
public:
    bool validPath(int n, vector<vector<int>>& edges, int source, int destination) {
        init(n);
        for(int i = 0;i < edges.size();i++){
            join(edges[i][0],edges[i][1]);
        }
        return isSame(source,destination);
    }
};

684.冗余连接

其实做的事就是不断的搭桥，直到哪个用不上，就return。

class Solution {
private:
    int nMax = 1005;
    vector<int>father = vector<int>(nMax,0);
    void init(){
        for(int i = 0;i < nMax;i++){
            father[i] = i;
        }
    }
    int find(int x){
        return x == father[x]? x : father[x] = find(father[x]);
    }
    bool isSame(int a , int b){
        a = find(a);
        b = find(b);
        return a == b;
    }
    void join(int a , int b){
        a = find(a);
        b = find(b);
        if(a == b)return;
        father[b] = a;
    }

public:
    vector<int> findRedundantConnection(vector<vector<int>>& edges) {
        init();
        for(int i = 0; i < edges.size();i++){
            if(isSame(edges[i][0],edges[i][1]))return edges[i];
            else join(edges[i][0],edges[i][1]);
        }
        return {};
    }
};

685.冗余连接II

有点难的那种，今天有点晚啦，先洗澡去啦，后面补上。