Buggy python submission (verdict: Time Limit Exceeded):
import sys
input = sys.stdin.readline

n = int(input())
A = list(map(int,input().split()))

dp = [[-float("INF")]*(n+1) for i in range(n+1)]
low = [-float("INF")]*(n+1)
col = [-float("INF")]*(n+1)
m = 0
a,b = A[:2]
dp[a][b] = 0
dp[b][a] = 0
low[a] = 0
col[a] = 0
low[b]
col[b] = 0
base = 0

for _ in range(1,n):
    a,b,c = A[3*_-1:3*_+2]
    q = []
    if a==b==c:
        base += 1
        continue
    for j in range(3):
        q.append((a,b,max(m,dp[c][c]+1)))
        for i in range(1,n+1):
            q.append((a,i,low[i]))
        if a==b:
            for i in range(1,n+1):
                q.append((c,i,dp[a][i]+1))
        a,b,c = b,c,a
    for a,b,v in q:
        dp[a][b] = max(dp[a][b],v)
        dp[b][a] = max(dp[b][a],v)
        low[a] = max(low[a],v)  
        low[b] = max(low[b],v)  
        col[a] = max(col[a],v)  
        col[b] = max(col[b],v) 
        m = max(m,v)     
print(max(m,dp[A[-1]][A[-1]]+1)+base)


Fixed submission:
import sys
input = sys.stdin.readline

n = int(input())
A = list(map(int,input().split()))

dp = [[-float("INF")]*(n+1) for i in range(n+1)]
low = [-float("INF")]*(n+1)
m = 0
a,b = A[:2]
dp[a][b] = 0
dp[b][a] = 0
low[a] = 0
low[b] = 0
base = 0

for _ in range(1,n):
    a,b,c = A[3*_-1:3*_+2]
    q = []
    if a==b==c:
        base += 1
        continue
    m1 = max(m,max(dp[a][a],dp[b][b],dp[c][c])+1)
    for j in range(3):
        q.append((a,b,max(m,dp[c][c]+1)))
        for i in range(1,n+1):
            q.append((a,i,low[i]))
        if a==b:
            for i in range(1,n+1):
                q.append((c,i,dp[a][i]+1))
                m1 = max(m1,dp[a][i]+1)
        a,b,c = b,c,a
    for a,b,v in q:
        dp[a][b] = max(dp[a][b],v)
        dp[b][a] = max(dp[b][a],v)
        low[a] = max(low[a],v)  
        low[b] = max(low[b],v)      
    m = m1
print(max(m,dp[A[-1]][A[-1]]+1)+base)

Buggy python submission (verdict: Time Limit Exceeded):
import sys
input = sys.stdin.readline
def main():
    n = int(input())
    A = list(map(int,input().split()))

    dp = [[-float("INF")]*(n+1) for i in range(n+1)]
    low = [-float("INF")]*(n+1)
    col = [-float("INF")]*(n+1)
    m = 0
    a,b = A[:2]
    dp[a][b] = 0
    dp[b][a] = 0
    low[a] = 0
    col[a] = 0
    low[b]
    col[b] = 0
    base = 0

    for _ in range(1,n):
        a,b,c = A[3*_-1:3*_+2]
        q = []
        if a==b==c:
            base += 1
            continue
        for j in range(3):
            q.append((a,b,max(m,dp[c][c]+1)))
            for i in range(1,n+1):
                q.append((a,i,low[i]))
            if a==b:
                for i in range(1,n+1):
                    q.append((c,i,dp[a][i]+1))
            a,b,c = b,c,a
        for a,b,v in q:
            dp[a][b] = max(dp[a][b],v)
            dp[b][a] = max(dp[b][a],v)
            low[a] = max(low[a],v)  
            low[b] = max(low[b],v)  
            col[a] = max(col[a],v)  
            col[b] = max(col[b],v) 
            m = max(m,v)     
    print(max(m,dp[A[-1]][A[-1]]+1)+base)
if __name__ == "__main__":
    main()

Fixed submission:
import sys
input = sys.stdin.readline

n = int(input())
A = list(map(int,input().split()))

dp = [[-float("INF")]*(n+1) for i in range(n+1)]
low = [-float("INF")]*(n+1)
m = 0
a,b = A[:2]
dp[a][b] = 0
dp[b][a] = 0
low[a] = 0
low[b] = 0
base = 0

for _ in range(1,n):
    a,b,c = A[3*_-1:3*_+2]
    q = []
    if a==b==c:
        base += 1
        continue
    m1 = max(m,max(dp[a][a],dp[b][b],dp[c][c])+1)
    for j in range(3):
        q.append((a,b,max(m,dp[c][c]+1)))
        for i in range(1,n+1):
            q.append((a,i,low[i]))
        if a==b:
            for i in range(1,n+1):
                q.append((c,i,dp[a][i]+1))
                m1 = max(m1,dp[a][i]+1)
        a,b,c = b,c,a
    for a,b,v in q:
        dp[a][b] = max(dp[a][b],v)
        dp[b][a] = max(dp[b][a],v)
        low[a] = max(low[a],v)  
        low[b] = max(low[b],v)      
    m = m1
print(max(m,dp[A[-1]][A[-1]]+1)+base)

Buggy python submission (verdict: Time Limit Exceeded):
n = int(input())
A = list(map(int,input().split()))

dp = [[-float("INF")]*(n+1) for i in range(n+1)]
low = [-float("INF")]*(n+1)
col = [-float("INF")]*(n+1)
m = 0
a,b = A[:2]
dp[a][b] = 0
dp[b][a] = 0
low[a] = 0
col[a] = 0
low[b]
col[b] = 0
base = 0

for _ in range(1,n):
    a,b,c = A[3*_-1:3*_+2]
    q = []
    if a==b==c:
        base += 1
        continue
    for j in range(3):
        q.append((a,b,max(m,dp[c][c]+1)))
        for i in range(1,n+1):
            q.append((a,i,low[i]))
        if a==b:
            for i in range(1,n+1):
                q.append((c,i,dp[a][i]+1))
        a,b,c = b,c,a
    for a,b,v in q:
        dp[a][b] = max(dp[a][b],v)
        dp[b][a] = max(dp[b][a],v)
        low[a] = max(low[a],v)  
        low[b] = max(low[b],v)  
        col[a] = max(col[a],v)  
        col[b] = max(col[b],v) 
        m = max(m,v)     
print(max(m,dp[A[-1]][A[-1]]+1)+base)


Fixed submission:
import sys
input = sys.stdin.readline

n = int(input())
A = list(map(int,input().split()))

dp = [[-float("INF")]*(n+1) for i in range(n+1)]
low = [-float("INF")]*(n+1)
m = 0
a,b = A[:2]
dp[a][b] = 0
dp[b][a] = 0
low[a] = 0
low[b] = 0
base = 0

for _ in range(1,n):
    a,b,c = A[3*_-1:3*_+2]
    q = []
    if a==b==c:
        base += 1
        continue
    m1 = max(m,max(dp[a][a],dp[b][b],dp[c][c])+1)
    for j in range(3):
        q.append((a,b,max(m,dp[c][c]+1)))
        for i in range(1,n+1):
            q.append((a,i,low[i]))
        if a==b:
            for i in range(1,n+1):
                q.append((c,i,dp[a][i]+1))
                m1 = max(m1,dp[a][i]+1)
        a,b,c = b,c,a
    for a,b,v in q:
        dp[a][b] = max(dp[a][b],v)
        dp[b][a] = max(dp[b][a],v)
        low[a] = max(low[a],v)  
        low[b] = max(low[b],v)      
    m = m1
print(max(m,dp[A[-1]][A[-1]]+1)+base)

Buggy python submission (verdict: Runtime Error):
n = int(input())
A = list(map(int,input().split()))

dp = [[-2]*(n+1) for i in range(n+1)]
low = [-2]*(n+1)
col = [-2]*(n+1)
m = 0
dp[A[0]][A[1]] = 0
low[A[0]] = 0
col[A[1]] = 0
base = 0

for _ in range(1,n):
    a,b,c = A[3*_-1:3*_+2]
    q = []
    if a==b==c:
        base += 1
        continue
    if a==b or b==c or c==a:
        if b==c:
            a,b,c = b,c,a
        elif c==a:
            a,b,c = a,c,b
        v = max(m,dp[c][c]+1)
        q.append((3,a,a,v))
        q.append((0,a,v))
        q.append((1,a,v))
        v1 = -2
        for i in range(1,n+1):
            if max(low[i],dp[i][a]+1)>= 0:
                dp[i][c] = max(dp[i][c],low[i],dp[i][a]+1)
                v1 = max(v1,dp[i][c])
                if dp[i][c] > low[i]:
                    q.append((0,i,dp[i][c]))
        q.append((1,c,v1))
        v2 = -2
        for i in range(1,n+1):
            if max(col[i],dp[a][i]+1)>= 0:
                dp[c][i] = max(dp[c][i],col[i],dp[a][i]+1)
                v2 = max(v2,dp[c][i])
                if dp[c][i] > col[i]:
                    q.append((1,i,dp[c][i]))
        q.append((0,c,v2))
        q.append((2,0,max(v,v1,v2)))
    
    else:
        for j in range(3):
            v = max(m,dp[c][c]+1)
            q.append((3,a,b,v))
            q.append((0,a,v))
            q.append((1,a,v))
            
            for i in range(1,n+1):
                if low[i]>= 0:
                    dp[i][c] = low[i]
        
            for i in range(1,n+1):
                if col[i]>= 0:
                    dp[c][i] = col[i]
   
            q.append((2,0,max(v,v1,v2)))

            a,b,c = b,c,a
    for l in q:
        if l[0] == 0:
            low[l[1]] = max(low[l[1]],l[2])
        elif l[0] == 1:
            col[l[1]] = max(col[l[1]],l[2])
        elif l[0] == 2:
            m = max(m,l[2])
        else:
            dp[l[1]][l[2]] = max(dp[l[1]][l[2]],l[3])
        
print(max(m,dp[A[-1]][A[-1]]+1)+base)

Fixed submission:
import sys
input = sys.stdin.readline

n = int(input())
A = list(map(int,input().split()))

dp = [[-float("INF")]*(n+1) for i in range(n+1)]
low = [-float("INF")]*(n+1)
m = 0
a,b = A[:2]
dp[a][b] = 0
dp[b][a] = 0
low[a] = 0
low[b] = 0
base = 0

for _ in range(1,n):
    a,b,c = A[3*_-1:3*_+2]
    q = []
    if a==b==c:
        base += 1
        continue
    m1 = max(m,max(dp[a][a],dp[b][b],dp[c][c])+1)
    for j in range(3):
        q.append((a,b,max(m,dp[c][c]+1)))
        for i in range(1,n+1):
            q.append((a,i,low[i]))
        if a==b:
            for i in range(1,n+1):
                q.append((c,i,dp[a][i]+1))
                m1 = max(m1,dp[a][i]+1)
        a,b,c = b,c,a
    for a,b,v in q:
        dp[a][b] = max(dp[a][b],v)
        dp[b][a] = max(dp[b][a],v)
        low[a] = max(low[a],v)  
        low[b] = max(low[b],v)      
    m = m1
print(max(m,dp[A[-1]][A[-1]]+1)+base)