Problem: 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.

Submission attempts (in order):
N = int(input())
C = [-1]

prev = -1
for _ in range(N):
    c = int(input())
    if c == prev:
        continue
    else:
        C.append(c)
        prev = c

MOD = 10**9+7
n = len(C)
dp = [0]*(n+2)
last = [-1]*(N*10)
dp[0] = 1
for i in range(1, n+1):
    if last[C[i]] == -1:
        last[C[i]] = i
        dp[i] = dp[i-1]
    else:
        dp[i] = dp[i-1]+dp[last[C[i]]]
        dp[i] %= MOD
        last[C[i]] = i
print(max(dp))


N = int(input())
C = [0]

prev = -1
for _ in range(N):
    c = int(input())
    if c == prev:
        continue
    else:
        C.append(c)
        prev = c

MOD = 10**9+7
dp = [0]*(N+1)
last = [-1]*(N+1)
dp[0] = 1
for i in range(1, len(C)):
    if last[C[i]] == -1:
        last[C[i]] = i
        dp[i] = dp[i-1]
    else:
        dp[i] = dp[i-1]+dp[last[C[i]]]
        dp[i] %= MOD
        last[C[i]] = i
print(dp[-1])


N = int(input())
C = [-1]

prev = -1
for _ in range(N):
    c = int(input())
    if c == prev:
        continue
    else:
        C.append(c)
        prev = c

MOD = 10**9+7
n = len(C)
dp = [0]*(n+1)
last = [-1]*(N+1)
dp[0] = 1
for i in range(1, n+1):
    if last[C[i]] == -1:
        last[C[i]] = i
        dp[i] = dp[i-1]
    else:
        dp[i] = dp[i-1]+dp[last[C[i]]]
        dp[i] %= MOD
        last[C[i]] = i
print(max(dp))


N = int(input())
C = [-1]

prev = -1
for _ in range(N):
    c = int(input())
    if c == prev:
        continue
    else:
        C.append(c)
        prev = c

MOD = 10**9+7
n = len(C)
dp = [0]*(n+2)
last = [-1]*(N+N)
dp[0] = 1
for i in range(1, n+1):
    if last[C[i]] == -1:
        last[C[i]] = i
        dp[i] = dp[i-1]
    else:
        dp[i] = dp[i-1]+dp[last[C[i]]]
        dp[i] %= MOD
        last[C[i]] = i
print(max(dp))


from collections import Counter
# python template for atcoder1
import sys
sys.setrecursionlimit(10**9)
input = sys.stdin.readline

MOD = 10**9+7


def comb2(N):
    return int(N*(N-1)/2)


N = int(input())
prev = -1
Col = []
for _ in range(N):
    c = int(input())
    if c == prev:
        continue
    else:
        prev = c
        Col.append(c)


cntF = [0]*(N+1)
forward = [0]*len(Col+1)
for i, c in enumerate(Col):
    forward[i] = cntF[c]
    cntF[c] += 1

cntB = [0]*(N+1)
back = [0]*(len(Col)+1)
for i in reversed(range(len(Col))):
    c = Col[i]
    back[i] = cntB[c]
    cntB[c] += 1

ans = 1+sum(forward)
for i in range(1, len(Col)-1):
    ans = ans + forward[i]*back[i+1]
    ans %= MOD
print(ans)


N = int(input())
C = [0]

prev = -1
for _ in range(N):
    c = int(input())
    if c == prev:
        continue
    else:
        C.append(c)
        prev = c

MOD = 10**9+7
dp = [0]*(N+4)
last = [-1]*(N+4)
dp[0] = 1
for i in range(1, len(C)):
    if last[C[i]] == -1:
        last[C[i]] = i
        dp[i] = dp[i-1]
    else:
        dp[i] = dp[i-1]+dp[last[C[i]]]
        dp[i] %= MOD
        last[C[i]] = i
print(max(dp[-1]))


N = int(input())
C = [0]

prev = -1
for _ in range(N):
    c = int(input())
    if c == prev:
        continue
    else:
        C.append(c)
        prev = c

MOD = 10**9+7
dp = [0]*(max(C)+1)
last = [-1]*(max(C)+1)
dp[0] = 1
for i in range(1, len(C)):
    if last[C[i]] == -1:
        last[C[i]] = i
        dp[i] = dp[i-1]
    else:
        dp[i] = dp[i-1]+dp[last[C[i]]]
        dp[i] %= MOD
        last[C[i]] = i
print(max(dp))


N = int(input())
C = [-1]

for _ in range(N):
    c = int(input())
    if c == C[-1]:
        continue
    else:
        C.append(c)

MOD = 10**9+7
dp = 1
prev = [0]*(max(C)+1)

for c in enumerate(C[1:]):
    dp = (dp+prev[c]) % MOD
    prev[c] = dp
print(dp)


N = int(input())
C = [-1]

prev = -1
for _ in range(N):
    c = int(input())
    if c == prev:
        continue
    else:
        C.append(c)
        prev = c

MOD = 10**9+7
n = len(C)
dp = [0]*(n+1)
last = [-1]*(N+N)
dp[0] = 1
for i in range(1, n+1):
    if last[C[i]] == -1:
        last[C[i]] = i
        dp[i] = dp[i-1]
    else:
        dp[i] = dp[i-1]+dp[last[C[i]]]
        dp[i] %= MOD
        last[C[i]] = i
print(max(dp))


N = int(input())
C = [0]

prev = -1
for _ in range(N):
    c = int(input())
    if c == prev:
        continue
    else:
        C.append(c)
        prev = c

MOD = 10**9+7
n = len(C)
dp = [0]*(n+1)
last = [-1]*(n+1)
dp[0] = 1
for i in range(1, n):
    if last[C[i]] == -1:
        last[C[i]] = i
        dp[i] = dp[i-1]
    else:
        dp[i] = dp[i-1]+dp[last[C[i]]]
        dp[i] %= MOD
        last[C[i]] = i
print(dp[-1])


N = int(input())
C = [-1]

for _ in range(N):
    c = int(input())
    if c == C[-1]:
        continue
    else:
        C.append(c)

MOD = 10**9+7
dp = 1
prev = [0]*(max(C)+1)

for c in C[1:]:
    dp = (dp+prev[c]) % MOD
    prev[c] = dp
print(dp)


Verdicts: Runtime Error

Runtime Error

Runtime Error

Runtime Error

Runtime Error

Runtime Error

Runtime Error

Runtime Error

Runtime Error

Runtime Error

Accepted