CodeForces 407B 简单dp

 1 #include "iostream"
 2 #include "cstdio"
 3 #include "cstring"
 4 #include "algorithm"
 5 using namespace std;
 6 const __int64 mod = 1e9 + 7;
 7 __int64 dp[1010];
 8 int pos[1010], n;
 9 
10 int main()
11 {
12     int i, j;
13     scanf("%d", &n);
14     for(i = 1; i <= n; ++i)
15         scanf("%d", &pos[i]);
16     for(i = 2; i <= n + 1; ++i) {
17         dp[i] = (dp[i - 1] + 1 + (dp[i - 1] - dp[pos[i - 1]] + mod) + 1) % mod;
18     }
19     printf("%I64d\n", dp[n + 1]);
20 }