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):
from collections import defaultdict
from bisect import *
def solve():
    d = defaultdict(lambda: [])
    N = int(input())
    for i in range(N):
        a = int(input())
        d[a].append(i)
    selist = []
    ends = [-1]
    for l in d.values():
        for i in range(len(l)-1):
            if l[i+1]-1>l[i]:
                selist.append([l[i],l[i+1]])
                ends.append(l[i+1])
    selist = [[-1,-1]]+sorted(selist,key=lambda x:x[1])
    # s_ind = {}
    # for i,(s,e) in enumerate(selist):
        # e_ind[e] = i
    # ends = list(e_ind.keys())
    ends.sort()
    dp = [0]*(len(selist))
    for i in range(1,len(selist)):
        dp[i] = dp[i-1]+1
        ind = bisect_right(ends,selist[i][0])
        dp[i] += dp[ind-1]
    ans = dp[-1]+1
    ans %= mod
    return ans
print(solve())

from collections import defaultdict
from bisect import *
def solve():
  mod = 10**9+7
    d = defaultdict(lambda: [])
    N = int(input())
    for i in range(N):
        a = int(input())
        d[a].append(i)
    selist = []
    for l in d.values():
        for i in range(len(l)-1):
            if l[i+1]-1>l[i]:
                selist.append([l[i],l[i+1]-1])
    start_sort = sorted(selist)
    e_ind = {}
    for i,(s,e) in enumerate(start_sort):
        e_ind[e] = i
    ends = list(e_ind.keys())
    ends.sort()
    dp = [0]*(len(selist)+1)
    for i in range(1,len(selist)+1):
        dp[i] = dp[i-1]+1
        ind = bisect_left(ends,selist[i-1][0])
        if ind>0:
            j = e_ind[ends[ind-1]]
            dp[i] += dp[j+1]
            dp[i] %= mod
    ans = dp[-1]+1
    ans %= mod
    return ans
print(solve())


from collections import defaultdict
from bisect import *
def solve():
  	mod = 10**9+7
    d = defaultdict(lambda: [])
    N = int(input())
    for i in range(N):
        a = int(input())
        d[a].append(i)
    selist = []
    for l in d.values():
        for i in range(len(l)-1):
            if l[i+1]-1>l[i]:
                selist.append([l[i],l[i+1]-1])
    start_sort = sorted(selist)
    e_ind = {}
    for i,(s,e) in enumerate(start_sort):
        e_ind[e] = i
    ends = list(e_ind.keys())
    ends.sort()
    dp = [0]*(len(selist)+1)
    for i in range(1,len(selist)+1):
        dp[i] = dp[i-1]+1
        ind = bisect_left(ends,selist[i-1][0])
        if ind>0:
            j = e_ind[ends[ind-1]]
            dp[i] += dp[j+1]
            dp[i] %= mod
    ans = dp[-1]+1
    ans %= mod
    return ans
print(solve())

from collections import defaultdict
from bisect import *
def solve():
    mod = 10**9+7
    d = defaultdict(lambda: [])
    N = int(input())
    for i in range(N):
        a = int(input())
        d[a].append(i)
    selist = [[-1,-1]]
    ends = [-1]
    for l in d.values():
        for i in range(len(l)-1):
            if l[i+1]-1>l[i]:
                selist.append([l[i],l[i+1]])
                ends.append(l[i+1])
    selist = sorted(selist,key=lambda x:x[1])
    ends.sort()
    dp = [0]*(len(selist))
    for i in range(1,len(selist)):
        dp[i] = dp[i-1]+1
        ind = bisect_right(ends,selist[i][0])
        dp[i] += dp[ind-1]
        dp[i] %= mod
    ans = dp[-1]+1
    ans %= mod
    return ans
print(solve())


Verdicts: Runtime Error

Runtime Error

Runtime Error

Accepted