onlyone's blog

By onlyone, 9 years ago, , Problem A:
Check whether exist a pair i and j,they satisfy xi+di = xj && xj+dj = xi;

Problem B:
Pay attention to Just Right or Red. use Div and Mod can solve it easily;

Problem C:
As we know, there are only two path -- forward and reverse, so we can do DFS from the one-degree nodes (only two nodes).
As their index may be very larger, so I used map<int,int> to do hash.

void dfs(int i)
{
int sz = mat[i].size()-1, j;
UF(j,0,sz)
if (!vis[mat[i][j]])
{
vis[mat[i][j]] = 1;
printf(" %d",val[mat[i][j]]);
dfs(mat[i][j]);
}
}

Problem D:
Floyd.
First, Floyd pretreat the path from I to J, and save the path.
Then get the answer.
The order is a1,a2...ak, K is the number of the leaves, we can assume a0 = ak+1 = 1, the root.
then, answer push_back the path[ai][ai+1].

if the ans.size() > 2*N-1 , cout -1;
else cout the answer.   Comments (9)
 Can you please describe your approach about problem D in more details. I didn't understand your approach.
•  first, i use floyd save all the path[i][j], vector path[][];path[i][j], from i to j;then, just push all the path, from 1 to next leaf, and come back 1.
 » About problem D. Since the route between two nodes in a tree can be split into two parts by their least common ancestor, I think maybe a better solution would using directly walk between two adjacent nodes by passing their lca and connect the edges.Although, since n is small enough, Floyd is just good for it. :-)
 » can anyone post the idea for 29E
•  » » It's a shortest path problem. The state is u, v, t, which means person 0 is at vertex u, person 1 is at vertex v, and person t must move now. For t = 1, you have to check that the vertex you move to is different from u. You can solve it with BFS.
•  » » » Thank you very much
•  » » » Thanks. That was really helpful.
 » why should we use map ?
•  » » Assuming the question is for C, the range of numbers is from 1 to 10^9 which means to store graph you will use an array of size 10^9 which is beyond the memory limit of your hardware.