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++14 (GCC 5.4.1) (judge verdict: Accepted)

#pragma GCC optimize ("O3")

#include <iostream>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <map>
#include <unordered_map>
#include <set>
#include <unordered_set>
#include <queue>
#include <set>
#include <algorithm>
#include <numeric>
using namespace std;

using QWORD  = uint64_t;
using SQWORD = int64_t;
using DWORD  = uint32_t;
using SDWORD = int32_t;
using WORD   = uint16_t;
using SWORD  = int16_t;
using BYTE   = uint8_t;
using SBYTE  = int8_t;
using DOUBLE = double;
using FLOAT  = float;

#define MIN_SDWORD (-2147483648)
#define MAX_SDWORD (2147483647)
#define MIN_SBYTE (-128)
#define MAX_SBYTE (127)

#define MIN_SQWORD (0x8000000000000000)
#define MAX_SQWORD (0x7FFFFFFFFFFFFFFF)

#define MAX_QWORD  (0xFFFFFFFFFFFFFFFF)
#define MAX_DWORD  (0xFFFFFFFF)
#define MAX_WORD   (0xFFFF)
#define MAX_BYTE   (0xFF)


#define ArrayLength(a)  (sizeof(a) / sizeof(a[0]))

static inline QWORD MAX(QWORD a, QWORD b) { return a > b ? a : b; }
static inline DWORD MAX(DWORD a, DWORD b) { return a > b ? a : b; }
static inline SDWORD MAX(SDWORD a, SDWORD b) { return a > b ? a : b; }
static inline QWORD MIN(QWORD a, QWORD b) { return a < b ? a : b; }
static inline DWORD MIN(DWORD a, DWORD b) { return a < b ? a : b; }
static inline SDWORD MIN(SDWORD a, SDWORD b) { return a < b ? a : b; }

#define BYTE_BITS   (8)
#define WORD_BITS   (16)
#define DWORD_BITS  (32)
#define QWORD_BITS  (64)

using M_BOOL = bool;
#define M_TRUE (true)
#define M_FALSE (false)
#define DIVISOR (1000000007)

static inline void inputString(char *pcStr)
{
    char *pcCur = pcStr;
    for (;;) {
        char c = getchar();
        if (('\n' == c) || (EOF == c)) {
            break;
        }
        *pcCur = c;
        pcCur++;
    }
    *pcCur = '\0';
}


static inline SQWORD inputSQWORD(void)
{
    SQWORD sqNumber = 0;
    SQWORD sqMultiplier = 1;
    M_BOOL bRead = M_FALSE;
    for (;;) {
        char c = getchar();
        if (!bRead) {
            if ('-' == c) {
                sqMultiplier = -1;
            }
        }
        if (('0' <= c) && (c <= '9')) {
            sqNumber *= 10LL;
            sqNumber += (SQWORD)(c - '0');
            bRead = M_TRUE;
        } else {
            if (bRead) {
                return sqNumber * sqMultiplier;
            }
        }
    }
}


static inline SDWORD inputSDWORD(void)
{
    SDWORD lNumber = 0;
    SDWORD lMultiplier = 1;
    M_BOOL bRead = M_FALSE;
    for (;;) {
        char c = getchar();
        if (!bRead) {
            if ('-' == c) {
                lMultiplier = -1;
            }
        }
        if (('0' <= c) && (c <= '9')) {
            lNumber *= 10;
            lNumber += (c - '0');
            bRead = M_TRUE;
        } else {
            if (bRead) {
                return lNumber * lMultiplier;
            }
        }
    }
}

static inline DOUBLE inputFP(void)
{
    DOUBLE dInt = 0.0;
    DOUBLE dFrac = 0.0;
    DOUBLE dMultiplier = 1.0;
    DWORD dwFpCnt = 0;
    DOUBLE *pdCur = &dInt;
    M_BOOL bRead = M_FALSE;
    for (;;) {
        char c = getchar();
        if (!bRead) {
            if ('-' == c) {
                dMultiplier = -1;
            }
        }
        if ('.' == c) {
            pdCur = &dFrac;
        } else if (('0' <= c) && (c <= '9')) {
            (*pdCur) *= 10;
            (*pdCur) += (DOUBLE)(c - '0');
            bRead = M_TRUE;
            if (pdCur == &dFrac) {
                dwFpCnt++;
            }
        } else {
            if (bRead) {
                return dMultiplier * (dInt + dFrac / (pow((DOUBLE)10.0 , (DOUBLE)dwFpCnt)));
            }
        }
    }
}


#define MAX_STONES  (200000)
#define MAX_COLOR   (200000)
static SQWORD s_asqLeftCnt[MAX_COLOR + 1];
static SQWORD s_asqLastIdx[MAX_STONES + 1];
static SQWORD s_asqCumSum[MAX_STONES + 1];
#define ANS_MOD         (1000000007)


int main()
{
    SQWORD sqInput_N = inputSQWORD();
    SQWORD sqCumSumCur = 0;
    SQWORD sqLastColor = 0;
    for (SQWORD sqIdx = 1; sqIdx <= sqInput_N; sqIdx++) {
        SQWORD sqColor = inputSQWORD();

        if (sqLastColor != sqColor) {
            if (0 < s_asqLastIdx[sqColor]) {
                SQWORD sqPairIdx = s_asqLastIdx[sqColor];
                SQWORD sqPairIncrease = s_asqCumSum[sqPairIdx] + 1;
//                SQWORD sqPairIncrease = s_asqLeftCnt[sqColor] + 1;
//                printf("idx[%lld] p: color[%lld], pair[%lld], inc[%lld]\n", sqIdx, sqColor, sqPairIdx, sqPairIncrease);

                s_asqCumSum[sqIdx] = (s_asqCumSum[sqIdx - 1] + sqPairIncrease) % ANS_MOD;
//                s_asqLeftCnt[sqColor] = s_asqLeftCnt[sqColor] + s_asqCumSum[sqIdx];
//                printf("  sum[%lld], left[%lld]\n", s_asqCumSum[sqIdx], s_asqLeftCnt[sqColor]);
            } else {
                s_asqCumSum[sqIdx] = s_asqCumSum[sqIdx - 1];
//                s_asqLeftCnt[sqColor] = s_asqCumSum[sqIdx];
//                printf("idx[%lld]\n", sqIdx);
//                printf("  sum[%lld], left[%lld]\n", s_asqCumSum[sqIdx], s_asqLeftCnt[sqColor]);
            }
            /* update last idx */
            s_asqLastIdx[sqColor] = sqIdx;
        } else {
            s_asqCumSum[sqIdx] = s_asqCumSum[sqIdx - 1];
//            s_asqLeftCnt[sqColor] = s_asqCumSum[sqIdx];
//            printf("idx[%lld]\n", sqIdx);
//            printf("  sum[%lld], left[%lld]\n", s_asqCumSum[sqIdx], s_asqLeftCnt[sqColor]);
        }

        sqLastColor = sqColor;
    }
    printf("%lld\n", (s_asqCumSum[sqInput_N] + 1) % ANS_MOD);

    return 0;
}