SleepingSchedule.cpp

/*
Code Forces #627 E
Sleeping Schedule

time limit per test: 2 seconds
memory limit per test: 256 megabytes
input: standard input
output: standard output

Vova had a pretty weird sleeping schedule. There are h hours in a day.
Vova will sleep exactly n times. The i-th time he will sleep exactly after ai hours from the time he woke up.
You can assume that Vova woke up exactly at the beginning of this story (the initial time is 0).
Each time Vova sleeps exactly one day (in other words, h hours).

Vova thinks that the i-th sleeping time is good if he starts to sleep between hours l and r inclusive.

Vova can control himself and before the i-th time can choose between two options:
go to sleep after ai hours or after ai−1 hours.

Your task is to say the maximum number of good sleeping times Vova can obtain if he acts optimally.

Input
The first line of the input contains four integers n,h,l and r (1≤n≤2000,3≤h≤2000,0≤l≤r<h) — the number of
times Vova goes to sleep, the number of hours in a day and the segment of the good sleeping time.

The second line of the input contains n integers a1,a2,…,an (1≤ai<h), where ai is the number of hours
after which Vova goes to sleep the i-th time.

Output
Print one integer — the maximum number of good sleeping times Vova can obtain if he acts optimally.

Example:

input

7 24 21 23
16 17 14 20 20 11 22

output

3

Note
The maximum number of good times in the example is 3.

The story starts from t=0.
Then Vova goes to sleep after a1−1 hours, now the time is 15. This time is not good.
Then Vova goes to sleep after a2−1 hours, now the time is 15+16=7. This time is also not good.
Then Vova goes to sleep after a3 hours, now the time is 7+14=21. This time is good.
Then Vova goes to sleep after a4−1 hours, now the time is 21+19=16. This time is not good.
Then Vova goes to sleep after a5 hours, now the time is 16+20=12. This time is not good.
Then Vova goes to sleep after a6 hours, now the time is 12+11=23. This time is good.
Then Vova goes to sleep after a7 hours, now the time is 23+22=21. This time is also good.

*/

#include<bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds;
using namespace std;
 
#define ff              first
#define ss              second
#define int             long long
#define pb              push_back
#define mp              make_pair
#define pii             pair<int,int>
#define vi              vector<int>
#define mii             map<int,int>
#define pqb             priority_queue<int>
#define pqs             priority_queue<int,vi,greater<int> >
#define setbits(x)      __builtin_popcountll(x)
#define zrobits(x)      __builtin_ctzll(x)
#define mod             1000000007
#define inf             1e18
#define ps(x,y)         fixed<<setprecision(y)<<x
#define mk(arr,n,type)  type *arr=new type[n];
#define w(x)            int x; cin>>x; while(x--)
#define pw(b,p)         pow(b,p) + 0.1
mt19937                 rng(chrono::steady_clock::now().time_since_epoch().count());
 
typedef tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update> pbds;
 
 
void c_p_c()
{
	ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#ifndef ONLINE_JUDGE
	freopen("input.txt", "r", stdin);
	freopen("output.txt", "w", stdout);
#endif
}
 
int dp[2001][2001];
int a[2001];
 
int32_t main()
{
	c_p_c();
	int n, h, l, r; 
    cin >> n >> h >> l >> r;
     
	dp[0][0] = 0;
 
	for (int i = 1; i < h; ++i)
		dp[0][i] = -1;
 
 
	for (int i = 1; i <= n; ++i)
		cin >> a[i];
 
 
	for (int i = 0; i < n; ++i){
		for (int hr = 0; hr < h; ++hr){
			dp[i + 1][hr] = -1;
		}
 
		for (int hr = 0; hr < h; ++hr){
			if (dp[i][hr] == -1)
				continue;
 
			int h1 = (hr + a[i + 1] - 1 + h) % h;
			int h2 = (hr + a[i + 1]) % h;
 
			dp[i + 1][h1] = max(dp[i + 1][h1], dp[i][hr] + (l <= h1 && h1 <= r));
			dp[i + 1][h2] = max(dp[i + 1][h2], dp[i][hr] + (l <= h2 && h2 <= r));
		}
	}
 
	int ans = 0;
 
	for (int i = 0; i < h; ++i)
		if (dp[n][i] != -1)
			ans = max(ans, dp[n][i]);
 
	cout << ans << '\n';
	return 0;
}