CF1821F.Timber
普及/提高-
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题目描述
There is a beautiful alley with trees in front of a shopping mall. Unfortunately, it has to go to make space for the parking lot.
The trees on the alley all grow in a single line. There are n spots for trees, index 0 is the shopping mall, index n+1 is the road and indices from 1 to n are the spots for trees. Some of them are taken — there grow trees of the same height k . No more than one tree grows in each spot.
When you chop down a tree in the spot x , you can make it fall either left or right. If it falls to the left, it takes up spots from x−k to x , inclusive. If it falls to the right, it takes up spots from x to x+k , inclusive.
Let m trees on the alley grow in some spots x1,x2,…,xm . Let an alley be called unfortunate if all m trees can be chopped down in such a way that:
- no tree falls on the shopping mall or the road;
- each spot is taken up by no more than one fallen tree.
Calculate the number of different unfortunate alleys with m trees of height k . Two alleys are considered different if there is a spot y such that a tree grows in y on the first alley and doesn't grow in y on the second alley.
Output the number modulo 998244353 .
输入格式
The only line contains three integers n,m and k ( 1≤m,k≤n≤3⋅105 ) — the number of spots for the trees, the number of trees and the height of each tree.
输出格式
Print a single integer — the number of different unfortunate alleys with m trees of height k , modulo 998244353 .
输入输出样例
输入#1
6 1 4
输出#1
4
输入#2
5 2 2
输出#2
0
输入#3
6 2 2
输出#3
4
输入#4
15 3 2
输出#4
311