Buggy python submission (verdict: Runtime Error):
import sys

mod = 10**9 + 7
N = int(sys.stdin.readline())

stones = []
for _ in range(N):
    stones.append(int(sys.stdin.readline()) - 1)

left = [-1 for _ in range(N+5)]
dp = [0 for _ in range(N+5)]
dp[0] = 1
for i in range(N):
    dp[i+1] = dp[i]
    # 同じ色が前回出現した位置
    c = stones[i]
    if 0 <= left[c] < i - 1:
        dp[i+1] += dp[left[c] + 1]
    
    dp[i+1] %= mod
    left[c] = i

print(dp[N])

Fixed submission:
import sys

mod = 10**9 + 7
N = int(sys.stdin.readline())

stones = []
for _ in range(N):
    stones.append(int(sys.stdin.readline()))

left = [-1 for _ in range(2*10**5+1)]
dp = [0 for _ in range(N+5)]
dp[0] = 1
for i in range(N):
    dp[i+1] = dp[i]
    # 同じ色が前回出現した位置
    c = stones[i]
    if 0 <= left[c] < i - 1:
        dp[i+1] += dp[left[c] + 1]
    
    dp[i+1] %= mod
    left[c] = i

print(dp[N])

Buggy python submission (verdict: Runtime Error):
import sys

mod = 10**9 + 7
N = int(sys.stdin.readline())

stones = []
for _ in range(N):
    stones.append(int(sys.stdin.readline()) - 1)

left = [-1 for _ in range(N)]
dp = [0 for _ in range(N+1)]
dp[0] = 1
for i in range(N):
    dp[i+1] = dp[i]
    # 同じ色が前回出現した位置
    c = stones[i]
    if 0 <= left[c] < i - 1:
        dp[i+1] += dp[left[c] + 1]
    
    dp[i+1] %= mod
    left[c] = i

print(dp[N])

Fixed submission:
import sys

mod = 10**9 + 7
N = int(sys.stdin.readline())

stones = []
for _ in range(N):
    stones.append(int(sys.stdin.readline()))

left = [-1 for _ in range(2*10**5+1)]
dp = [0 for _ in range(N+5)]
dp[0] = 1
for i in range(N):
    dp[i+1] = dp[i]
    # 同じ色が前回出現した位置
    c = stones[i]
    if 0 <= left[c] < i - 1:
        dp[i+1] += dp[left[c] + 1]
    
    dp[i+1] %= mod
    left[c] = i

print(dp[N])

Buggy python submission (verdict: Runtime Error):
import sys

mod = 10**9 + 7
N = int(sys.stdin.readline())

stones = []
for _ in range(N):
    stones.append(int(sys.stdin.readline()))

left = [-1 for _ in range(N+1)] # 1-indexed
dp = [0 for _ in range(N+1)]
dp[0] = 1
for i in range(N):
    dp[i+1] = dp[i]
    # 同じ色が前回出現した位置
    c = stones[i]
    if 0 <= left[c] < i - 1:
        dp[i+1] += dp[left[c] + 1]
    
    dp[i+1] %= mod
    left[c] = i

print(dp[N])

Fixed submission:
import sys

mod = 10**9 + 7
N = int(sys.stdin.readline())

stones = []
for _ in range(N):
    stones.append(int(sys.stdin.readline()))

left = [-1 for _ in range(2*10**5+1)]
dp = [0 for _ in range(N+5)]
dp[0] = 1
for i in range(N):
    dp[i+1] = dp[i]
    # 同じ色が前回出現した位置
    c = stones[i]
    if 0 <= left[c] < i - 1:
        dp[i+1] += dp[left[c] + 1]
    
    dp[i+1] %= mod
    left[c] = i

print(dp[N])

Buggy python submission (verdict: Runtime Error):
import sys

mod = 10**9 + 7
N = int(sys.stdin.readline())

stones = []
for _ in range(N):
    stones.append(int(sys.stdin.readline()))

left = [-1] * (N+1) # 1-indexed
dp = [0] * (N+1)
dp[0] = 1
for i in range(N):
    dp[i+1] = dp[i]
    # 同じ色が前回出現した位置
    c = stones[i]
    if 0 <= left[c] < i - 1:
        dp[i+1] += dp[left[c] + 1]
    
    dp[i+1] %= mod
    left[stones[i]] = i

print(dp[N])

Fixed submission:
import sys

mod = 10**9 + 7
N = int(sys.stdin.readline())

stones = []
for _ in range(N):
    stones.append(int(sys.stdin.readline()))

left = [-1 for _ in range(2*10**5+1)]
dp = [0 for _ in range(N+5)]
dp[0] = 1
for i in range(N):
    dp[i+1] = dp[i]
    # 同じ色が前回出現した位置
    c = stones[i]
    if 0 <= left[c] < i - 1:
        dp[i+1] += dp[left[c] + 1]
    
    dp[i+1] %= mod
    left[c] = i

print(dp[N])

Buggy python submission (verdict: Runtime Error):
import sys

N = int(sys.stdin.readline())

stones = []
for _ in range(N):
    stones.append(int(sys.stdin.readline()))

left = [-1] * (N+1) # 1-indexed
dp = [0] * (N+1)
dp[0] = 1
for i in range(1, N+1):
    dp[i] = dp[i-1]
    # 同じ色が前回出現した位置
    if left[stones[i-1]] != -1 and left[stones[i-1]] != i - 1:
        dp[i] += dp[left[stones[i-1]]]
    
    left[stones[i-1]] = i

print(dp[-1])

Fixed submission:
import sys

mod = 10**9 + 7
N = int(sys.stdin.readline())

stones = []
for _ in range(N):
    stones.append(int(sys.stdin.readline()))

left = [-1 for _ in range(2*10**5+1)]
dp = [0 for _ in range(N+5)]
dp[0] = 1
for i in range(N):
    dp[i+1] = dp[i]
    # 同じ色が前回出現した位置
    c = stones[i]
    if 0 <= left[c] < i - 1:
        dp[i+1] += dp[left[c] + 1]
    
    dp[i+1] %= mod
    left[c] = i

print(dp[N])

Buggy python submission (verdict: Runtime Error):
import sys

N = int(sys.stdin.readline())

stones = []
for _ in range(N):
    stones.append(int(sys.stdin.readline()))

left = [-1] * N
dp = [0] * (N+1)
dp[0] = 1
for i in range(1, N+1):
    dp[i] = dp[i-1]
    # 同じ色が前回出現した位置
    if left[stones[i-1]] != -1 and left[stones[i-1]] != i - 1:
        dp[i] += dp[left[stones[i-1]]]
    
    left[stones[i-1]] = i

print(dp[-1])

Fixed submission:
import sys

mod = 10**9 + 7
N = int(sys.stdin.readline())

stones = []
for _ in range(N):
    stones.append(int(sys.stdin.readline()))

left = [-1 for _ in range(2*10**5+1)]
dp = [0 for _ in range(N+5)]
dp[0] = 1
for i in range(N):
    dp[i+1] = dp[i]
    # 同じ色が前回出現した位置
    c = stones[i]
    if 0 <= left[c] < i - 1:
        dp[i+1] += dp[left[c] + 1]
    
    dp[i+1] %= mod
    left[c] = i

print(dp[N])