NO4——并查集

 int find(int x)
 {
     int r = x;
     while(father[r]!=r)
     r = father[r];
     return r;
 }
 /*
 int find(int x)
 {
     if(father[x] == x)
     return x;
     else
     return father[x] =find(father[x]);
 }
 */

 void join(int x,int j)
 {
     int fx = find(x),fy = find(y);
     if(fx!=fy)
     father[fx] = fy;
 }

 void Union(int x,int y)
 {
     int rx,ry;
     rx = find(x);
     ry = find(y);
     father[rx] = ry;
 }