并查集 yongmou

void ufs_initialize(int n, int parent[]){
    /* initialize set -1 */
    for(int i=0; i<n; ++i)
        parent[i] = -1;
}

void ufs_union(int i, int j, int parent[]){
    /* union the sets with roots i and j, i != j, using the weighting rule. */
    if(parent[i] > parent[j]){
        parent[j] += parent[i];
        parent[i] = j;
    }
    else{
        parent[i] += parent[j];
        parent[j] = i;
    }
}

int ufs_find(int i, int parent[]){
    /* find the root of the tree containing element i.
       Use the collapsing rule to collapse all nodes from i to root */
    int root, trail, lead;
    for(root = i; parent[root]>=0; root=parent[root]) ;
    //collapse(压缩)
    trail = i;
    while(trail != root){
        lead = parent[trail];
        parent[trail] = root;
        trail = lead;
    }
    return root;
}