cses-solutions/array_description.cpp at main · sairohan0/cses-solutions · GitHub

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#include <bits/stdc++.h>

using namespace std;

int MOD = 1000000007;

int main() {
	int n, m;
	cin >> n >> m;
	vector<int> x(n);
	for(auto i=0;i<n;i++) {
		cin >> x[i];
	}
	vector<pair<pair<int,int>,int>> v;
	int answer = 1;
	int i = 0;
	while(i<=n) {
		if(x[i]==0) {
			int count = 0;
			while(i<n && x[i]==0) {
				i++;
				count++;
			}

			if(i==n) {v.push_back({{0,0},count}); break;}
			v.push_back({{0,x[i]},count});
			if(i==n-1) break;
		} else {
			int temp = x[i];
			int count = 0;
			i++;
			while(i<=n-1 && x[i]!=0) {
				i++;
				count++;
			}
			if(i==n) {v.push_back({{x[i],0},count}); break;}
			v.push_back({{temp,x[i]}, count});
			if(i==n-1) break;
		}
	}
	vector<vector<int>> dp_2(m+1, vector<int>(m+1,0));
	for(auto i=1;i<=m;i++) dp_2[0][i] = 1;
	for(auto i=1;i<=m;i++) {
		for(auto j=1;j<=m;j++) {
			if(j==m) dp_2[i][j] = dp_2[i-1][j] + dp_2[i-1][j-1];
			else dp_2[i][j] = ((dp_2[i-1][j] + dp_2[i-1][j-1])%MOD + dp_2[i-1][j+1])%MOD;

		}
	}

	for(auto &alpha:v) {
		if(alpha.first.first==0 && alpha.first.second==0) {
			int ss = 0;
			for(auto i=0;i<=m;i++) {
				ss = (ss+dp_2[m-1][i])%MOD;
			}
			answer = (answer*ss)%MOD;
		} else if(alpha.first.first==0) {
			answer = (answer*dp_2[alpha.second][alpha.first.second])%MOD;
		} else if(alpha.first.second==0) {
			answer = (answer*dp_2[alpha.second][alpha.first.first])%MOD;
		} else {
			int temp1, temp2;
			temp1 = max(alpha.first.first, alpha.first.second);
			temp2 = min(alpha.first.first, alpha.first.second);
			int count = alpha.second;
			vector<vector<int>> dp(count+1, vector<int>(temp1+2,0));
			for(auto j=temp2-1;j<=temp1+1 && j<=temp2+1;j++) {
				if(j!=0) {
					dp[0][j] = 1;
				}
			}
			for(auto i=1;i<=count;i++) {
				for(auto j=1;j<=temp1+1;j++) {
					if(j==temp2) dp[i][j] = (dp[i-1][j] + dp[i-1][j-1])%MOD;
					else dp[i][j] = ((dp[i-1][j]+dp[i-1][j-1])%MOD + dp[i-1][j+1])%MOD;
				}
			}
			answer = (answer*dp[count][temp2])%MOD;

		}
	}
	cout << answer << endl;
	return 0;
}