No.3220 Forest Creation
問題文最終更新日: 2026-10-22 21:32:17
English (AI translation)
This statement was translated by AI (claude-opus-5-5, effort medium) and may contain errors or differ in nuance from the original. The original statement takes precedence.
Back to the original
yukicoder contest 476
(順位表)
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Problem Statement
Kero-chan, an indigenous god, can create forests.
Kero-chan is trying to create a forest that satisfies the following conditions.
- For every $i(0\leq i\leq N)$, there are exactly $A_i$ vertices of degree $i$
- For $N<i$, the number of vertices of degree $i$ is $0$
Determine whether this is possible. Here, assume that Kero-chan can create any forest.
Note that a graph with no vertices is also considered a forest (when all $A_i$ are $0$, the answer is Yes).
More formal problem statement
Determine whether there exists an undirected graph $G$ that satisfies all of the following conditions.
- $G$ contains no cycles
- Letting $D_i$ be the number of vertices in $G$ whose degree is $i$, $A_i=D_i$ for every $i(0\leq i\leq N)$ and $D_i=0$ for $N<i$
About the red text
During the contest, the statement instead contained the sentence "For $N<i$, there is no constraint on the number of vertices of degree $i$." It has been corrected to the content in red.Since this could be interpreted as changing the problem itself in some cases, we are truly sorry to those who received a wrong verdict because of this.
- If interpreted as allowing any number of vertices of degree greater than $N$, cases such as $N=1, A=(0, 9)$ would also be
Yes, but the intent of the problem when it was written wasNo - Without mention of $N<i$ the statement was somewhat ambiguous, so a sentence was added, but it was worded incorrectly at that time, which led to this situation
Input
$N$ $A_0\ A_1\ A_2\ \cdots\ A_N$
- $1\leq N\leq 10^5$
- $0\leq A_i\leq 10^8$
- All inputs are integers
Output
Print Yes if a forest satisfying the conditions can be created, and No otherwise, on $1$ line.
Print a newline at the end.
Sample
Sample 1
Input
3 0 5 1 1
Output
Yes
For example, you can create the following graph.
o o / | o - o o - o - o
Sample 2
Input
2 0 0 3
Output
No
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