1202 子序列个数(DP)

 1  # include <cstdio>
 2 # include <cstring>
 3 # include <cstdlib>
 4 # include <iostream>
 5 # include <vector>
 6 # include <queue>
 7 # include <stack>
 8 # include <map>
 9 # include <bitset>
10 # include <sstream>
11 # include <set>
12 # include <cmath>
13 # include <algorithm>
14 # pragma  comment(linker,"/STACK:102400000,102400000")
15 using namespace std;
16 #define MOD 1000000007
17 #define INF 0x3f3f3f3f
18 #define LL long long
19 #define MX 100005
20 
21 int n;
22 int dat[MX];
23 int zhi[MX];
24 int pre[MX];
25 LL sum[MX];
26 LL dp[MX];
27 
28 int main()
29 {
30     scanf("%d",&n);
31     for (int i=1;i<=n;i++)
32     {
33         scanf("%d",dat+i);
34         pre[i] = zhi[dat[i]];
35         zhi[dat[i]] = i;
36     }
37     for (int i=1;i<=n;i++)
38     {
39         if (pre[i]==0)
40             dp[i] = (sum[i-1] + 1)%MOD;
41         else
42             dp[i] = (sum[i-1] - sum[pre[i]-1] + MOD)%MOD;
43         sum[i] = (sum[i-1] + dp[i])%MOD;
44     }
45     printf("%lld\n",sum[n]);
46     return 0;
47 }