Problem:
Score : 700 points

Problem Statement

There are N stones arranged in a row. The i-th stone from the left is painted in the color C_i.

Snuke will perform the following operation zero or more times:

Choose two stones painted in the same color. Repaint all the stones between them, with the color of the chosen stones.

Find the number of possible final sequences of colors of the stones, modulo 10^9+7.

Constraints

1 \leq N \leq 2\times 10^5

1 \leq C_i \leq 2\times 10^5(1\leq i\leq N)

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N
C_1
:
C_N

Output

Print the number of possible final sequences of colors of the stones, modulo 10^9+7.

Sample Input 1

5
1
2
1
2
2

Sample Output 1

3

We can make three sequences of colors of stones, as follows:

(1,2,1,2,2), by doing nothing.

(1,1,1,2,2), by choosing the first and third stones to perform the operation.

(1,2,2,2,2), by choosing the second and fourth stones to perform the operation.

Sample Input 2

6
4
2
5
4
2
4

Sample Output 2

5

Sample Input 3

7
1
3
1
2
3
3
2

Sample Output 3

5

Solution in Python (3.8.2) (judge verdict: Wrong Answer)

import sys,math,collections,itertools
input = sys.stdin.readline

N = int(input())
ans = 1
m=10**9+7
c=[]
for _ in range(N):
    c.append(int(input()))
dp = [1]*(N+1)#dp[i] i番目までの並び替え総数
last_color = [-1]*(max(c)+1)#最後にその色が出たindexの保存
last_color[c[0]] =1
for i in range(1,N):
    if c[i]==c[i-1]:#同じ色が続くとリバーシできない
        dp[i+1] = dp[i]
    else:
        if last_color[c[i]]==-1:#初めての色はリバーシできない
            dp[i+1] = dp[i]
            last_color[c[i]]=i
        else:#挟める石があるし色が連続してない
            dp[i+1] = dp[i]+dp[last_color[c[i]]]#最後に出た石と挟むか挟まないk
            last_color[c[i]]=i
print(dp[N])