PAT A 1013. Battle Over Cities (25)【并查集】

https://www.patest.cn/contests/pat-a-practise/1013

思路：并查集合并

#include<set>  
#include<map>  
#include<queue>  
#include<algorithm>  
#include<string>  
#include<string.h>  
using namespace std;

int n;//number of city  
int m;//number of edge  
int k;//number of query  

typedef struct  Edge
{
    int v;
    Edge(int _v) :v(_v){};
}Edge;
typedef struct Node
{
    int parent;
}Node;
vector<Node> city;
void InitSet()
{
    city.resize(n);
    for (int i = 0; i < n; i++)
        city[i].parent = i;//独立离散连通域
}

int FindSet(int x)
{
    if (city[x].parent != x)
    {
        int top = FindSet(city[x].parent);
        city[x].parent = top;
    }
    return city[x].parent;
}
void UnionSet(int x, int y)
{
    int a = FindSet(x);
    int b = FindSet(y);
    if (a != b)city[a].parent = b;
}
int main()
{
    scanf("%d%d%d", &n, &m, &k);
    vector<vector<Edge>> edge;
    edge.resize(n);
    for (int i = 0; i < m;i++)
    {
        int a, b;
        scanf("%d%d", &a, &b);
        a--, b--;
        edge[a].push_back(Edge(b));
        edge[b].push_back(Edge(a));
    }
    for (int i = 0; i < k; i++)
    {
        int q;
        scanf("%d", &q);
        q--;
        InitSet();
        for (int u = 0; u < n; u++)
        {
            for (int j = 0; j < edge[u].size(); j++)
            {
                int v = edge[u][j].v;
                if (u != q&&v != q)UnionSet(u, v);
            }
        }
        set<int> parentSet;
        for (int j = 0; j < n; ++j)
            //must be care for this, for consistency we must get the root via FindSet function instead of city[j].parent  
            parentSet.insert(FindSet(j));
        printf("%d
", parentSet.size() - 2);
    }
    return 0;
}