B. Destruction of a Tree
constructive algorithms; dfs and similar; dp; greedy; trees
You are given a tree (a graph with n vertices and n - 1 edges in which it's possible to reach any vertex from any other vertex using only its edges).A vertex can be destroyed if this vertex has even degree. If you destroy a vertex, all edges connected to it are also deleted.Destroy all vertices in the given tree or determine that it is impossible.
The first line contains integer n (1 ≤ n ≤ 2·105) — number of vertices in a tree.The second line contains n integers p1, p2, ..., pn (0 ≤ pi ≤ n). If pi ≠ 0 there is an edge between vertices i and pi. It is guaranteed that the given graph is a tree.
If it's possible to destroy all vertices, print ""YES"" (without quotes), otherwise print ""NO"" (without quotes).If it's possible to destroy all vertices, in the next n lines print the indices of the vertices in order you destroy them. If there are multiple correct answers, print any.
In the first example at first you have to remove the vertex with index 1 (after that, the edges (1, 2) and (1, 4) are removed), then the vertex with index 2 (and edges (2, 3) and (2, 5) are removed). After that there are no edges in the tree, so you can remove remaining vertices in any order.