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\n", parentSet.size() - 2);
}
return 0;
}