DP

http://exercise.acmcoder.com/online/online_judge_ques?ques_id=3862&konwledgeId=42

#include <bits/stdc++.h>
using namespace std;

#define maxn 100009
const int MOD = 1e9 + 7;
int main()
{
    int n;
    int a[maxn];
    int dp[maxn];
    int cnt[11];
    
    while (~scanf("%d",&n))
    {
        memset(a,0,sizeof(a));
        memset(dp,0,sizeof(dp));
        for (int i = 1;i<=n;i++)
        {
            scanf("%d",&a[i]);
        }
        dp[0] = 1;
        for (int i = 1;i<=n;i++)
        {
            memset(cnt,0,sizeof(cnt));
            for (int j = 0;j<i;j++)
            {
                cnt[a[i-j]]++;
                if (cnt[a[i-j]] > 1)
                {
                    break;
                }
                dp[i] = (dp[i] + dp[i-j-1])%MOD;
            }
        }
        printf("%d
",dp[n]);
    }
    return 0;
}

 https://hihocoder.com/problemset/problem/1482

#include <bits/stdc++.h>

using namespace std;
const int MOD = 1e9 + 7;

int dp[100000 + 1000][2][3];

long long Add(int a,int b)
{
    long long ans = (a+b)%MOD;
    return ans;
}
void Init()
{
    memset(dp,0,sizeof(dp));
    dp[0][0][0] = 1;
    for (int i = 0;i<100000;i++)
    {
        for (int j = 0;j<2;j++)
        {
            for (int k = 0;k<3;k++)
            {
                dp[i+1][j][0] = Add(dp[i+1][j][0],dp[i][j][k]);
                if (j != 1)
                {
                    dp[i+1][j+1][0] = Add(dp[i+1][j+1][0],dp[i][j][k]);
                }
                if (k != 2)
                {
                    dp[i+1][j][k+1] = Add(dp[i+1][j][k+1],dp[i][j][k]);
                }
            }
        }
    }
}
int main()
{
    int n;
    Init();
    while (~scanf("%d",&n))
    {
        int ans = 0;
        for (int i = 0;i<2;i++)
        {
            for (int j = 0;j<3;j++)
            {
            //printf("%d  ",dp[n][i][j]);
                ans = Add(ans,dp[n][i][j]);
            }
            
        }
        printf("%d
",ans);
    }
    return 0;
}