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 C (Clang 3.8.0) (judge verdict: Accepted)

#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <inttypes.h>
#include <ctype.h>
#include <stdint.h>
#include <string.h>
#include <wchar.h>

#define N_MAX (100)
#define P_MAX (100)
#define DP_ARRAY_SIZE (N_MAX * P_MAX / 32 + 1)

#define MIN(a, b) ((a) < (b) ? (a) : (b))
#define MAX(a, b) ((a) > (b) ? (a) : (b))
#define ABS(a) ((a) < 0 ? -(a) : (a))
#define ABSS(a, b) ((a) > (b) ? (a) - (b) : (b) - (a))

int compare_f(const void *a, const void *b) {
	return *((int64_t *)a) < *((int64_t *)b) ? -1 : 1;
}

int compare_f2(const void *a, const void *b) {
	return *((uint64_t *)a) > *((uint64_t *)b) ? -1 : 1;
}

static size_t comb(const size_t n, const size_t r) {
	size_t result = 1;

	for (size_t i = 0; i < r; i++) {
		result *= n - i;
		result /= i + 1;
	}

	return result;
}

static uint64_t gcd(uint64_t m, uint64_t n)
{
	uint64_t temp;

	while (m%n != 0) {
		temp = n;
		n = m % n;
		m = temp;
	}

	return n;
}

#define MOD_VAL (UINT64_C(1000000007))

#define LAST_POS_NONE ((size_t)1000000)

static uint64_t dp[200000];
static size_t lastPos[200000];

int main(void) {
	for (size_t i = 0; i < 200000; i++) {
		lastPos[i] = LAST_POS_NONE;
	}

	size_t N;
	size_t prevC = 0;

	scanf("%zu\n", &N);
	for (size_t i = 0; i < N; i++) {
		size_t C;

		scanf("%zu", &C);
		if (i < N - 1) {
			scanf("\n");
		}

		C--;
		
		if (i == 0) {
			dp[0] = 1;
		}
		else {
			if (lastPos[C] == LAST_POS_NONE) {
				dp[i] = dp[i - 1];
			}
			else {
				if (C == prevC) {
					dp[i] = dp[i - 1];
				}
				else {
					dp[i] = (dp[i - 1] + dp[lastPos[C]]) % MOD_VAL;
				}
			}
		}

		lastPos[C] = i;

		prevC = C;
	}

	printf("%"PRIu64, dp[N - 1]);

	return 0;
}