Buggy python submission (verdict: Time Limit Exceeded):
#!/usr/bin/env python3
import sys
import collections
import itertools


def solve(N: int, S: str):
    dp = [[0 for _ in range(N)] for _ in range(N)]

    for i in range(N):
        if S[i] == S[-1]:
            dp[i][N-1] = 1

    res = 0
    for i in range(N-2,-1,-1):
        for j in range(N-2,i,-1):
            if S[i] == S[j]:
                dp[i][j] = dp[i+1][j+1] + 1
                l = dp[i][j]
                if j >= i+l:
                    res = max(res,l)

    print(res)



# Generated by 1.1.4 https://github.com/kyuridenamida/atcoder-tools  (tips: You use the default template now. You can remove this line by using your custom template)
def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  # type: int
    S = next(tokens)  # type: str
    solve(N, S)

if __name__ == '__main__':
    main()


Fixed submission:
#!/usr/bin/env python3
import sys
import collections
import itertools


def solve(N: int, S: str):
    dp = [[0 for _ in range(N)] for _ in range(N)]

    for i in range(N):
        if S[i] == S[-1]:
            dp[i][N-1] = 1

    res = 0
    for i in range(N-2,-1,-1):
        for j in range(N-2,i,-1):
            if S[i] == S[j]:
                dp[i][j] = dp[i+1][j+1] + 1
                l = dp[i][j]
                if j >= i+l:
                    res = max(res,l)

    print(res)



# Generated by 1.1.4 https://github.com/kyuridenamida/atcoder-tools  (tips: You use the default template now. You can remove this line by using your custom template)
def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  # type: int
    S = next(tokens)  # type: str
    solve(N, S)

if __name__ == '__main__':
    main()

Buggy python submission (verdict: Time Limit Exceeded):
#!/usr/bin/env python3
import sys
import collections
import itertools


def solve(N: int, S: str):
    dp = [[0 for _ in range(N)] for _ in range(N)]

    for i in range(N):
        if S[i] == S[-1]:
            dp[N-1][i] = 1
            dp[i][N-1] = 1

    for i in range(N-2,-1,-1):
        for j in range(N-2,i,-1):
            if S[i] == S[j]:
                dp[i][j] = dp[i+1][j+1] + 1

    res = 0
    for i in range(N):
        for j in range(i+1,N):
            l = dp[i][j]
            if j >= i+l:
                res = max(res,l)

    print(res)



# Generated by 1.1.4 https://github.com/kyuridenamida/atcoder-tools  (tips: You use the default template now. You can remove this line by using your custom template)
def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  # type: int
    S = next(tokens)  # type: str
    solve(N, S)

if __name__ == '__main__':
    main()


Fixed submission:
#!/usr/bin/env python3
import sys
import collections
import itertools


def solve(N: int, S: str):
    dp = [[0 for _ in range(N)] for _ in range(N)]

    for i in range(N):
        if S[i] == S[-1]:
            dp[i][N-1] = 1

    res = 0
    for i in range(N-2,-1,-1):
        for j in range(N-2,i,-1):
            if S[i] == S[j]:
                dp[i][j] = dp[i+1][j+1] + 1
                l = dp[i][j]
                if j >= i+l:
                    res = max(res,l)

    print(res)



# Generated by 1.1.4 https://github.com/kyuridenamida/atcoder-tools  (tips: You use the default template now. You can remove this line by using your custom template)
def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  # type: int
    S = next(tokens)  # type: str
    solve(N, S)

if __name__ == '__main__':
    main()

Buggy python submission (verdict: Time Limit Exceeded):
#!/usr/bin/env python3
import sys
import collections
import itertools


def solve(N: int, S: str):
    dp = [[0 for _ in range(N)] for _ in range(N)]

    for i in range(N):
        if S[i] == S[-1]:
            dp[i][N-1] = 1

    for j in range(N):
        if S[j] == S[-1]:
            dp[N-1][j] = 1

    for i in range(N-2,-1,-1):
        for j in range(N-2,-1,-1):
            if S[i] == S[j]:
                dp[i][j] = dp[i+1][j+1] + 1

    res = 0
    for i in range(N):
        for j in range(i+1,N):
            l = dp[i][j]
            if j >= i+l:
                res = max(res,l)

    print(res)



# Generated by 1.1.4 https://github.com/kyuridenamida/atcoder-tools  (tips: You use the default template now. You can remove this line by using your custom template)
def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  # type: int
    S = next(tokens)  # type: str
    solve(N, S)

if __name__ == '__main__':
    main()


Fixed submission:
#!/usr/bin/env python3
import sys
import collections
import itertools


def solve(N: int, S: str):
    dp = [[0 for _ in range(N)] for _ in range(N)]

    for i in range(N):
        if S[i] == S[-1]:
            dp[i][N-1] = 1

    res = 0
    for i in range(N-2,-1,-1):
        for j in range(N-2,i,-1):
            if S[i] == S[j]:
                dp[i][j] = dp[i+1][j+1] + 1
                l = dp[i][j]
                if j >= i+l:
                    res = max(res,l)

    print(res)



# Generated by 1.1.4 https://github.com/kyuridenamida/atcoder-tools  (tips: You use the default template now. You can remove this line by using your custom template)
def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  # type: int
    S = next(tokens)  # type: str
    solve(N, S)

if __name__ == '__main__':
    main()

Buggy python submission (verdict: Time Limit Exceeded):
#!/usr/bin/env python3
import sys
import collections
import itertools


def solve(N: int, S: str):

    dp = collections.defaultdict(set)
    for i,s in enumerate(S):
        for k,v in list(dp.items()):
            for vv in v:
                if vv + len(k) == i:
                    dp[k+s].add(vv)
        dp[s].add(i)
    
    dp_sorted = sorted(((k,v) for k,v in dp.items() if len(v) > 1),key=lambda x:len(x[0]),reverse=True)

    for k,v in dp_sorted:
        if max(v) - min(v) >= len(k):
            print(len(k))
            return

    print(0)

def filter_dp(dp):
    return {k:v for k,v in dp.items() if len(v) > 1}

def solve2(N: int, S: str):
    dp = collections.defaultdict(set)

    for i,s in enumerate(S[:-1]):
        dp[S[i:i+2]].add(i)

    dp = filter_dp(dp)

    if len(dp) > 0:
        for i in range(2, N):
            dp2 = collections.defaultdict(set)
            for k,v in dp.items():
                for a, b in itertools.combinations(v,2):
                    a, b = sorted([a,b])
                    if b+i < N and a+i < b and S[a+i] == S[b+i]:
                        dp2[S[a:a+i+1]].add(a)
                        dp2[S[a:a+i+1]].add(b)
            if len(dp2):
                dp = dp2
            else:
                print(i)
                return

    print(0)

    



# Generated by 1.1.4 https://github.com/kyuridenamida/atcoder-tools  (tips: You use the default template now. You can remove this line by using your custom template)
def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  # type: int
    S = next(tokens)  # type: str
    solve2(N, S)

if __name__ == '__main__':
    main()


Fixed submission:
#!/usr/bin/env python3
import sys
import collections
import itertools


def solve(N: int, S: str):
    dp = [[0 for _ in range(N)] for _ in range(N)]

    for i in range(N):
        if S[i] == S[-1]:
            dp[i][N-1] = 1

    res = 0
    for i in range(N-2,-1,-1):
        for j in range(N-2,i,-1):
            if S[i] == S[j]:
                dp[i][j] = dp[i+1][j+1] + 1
                l = dp[i][j]
                if j >= i+l:
                    res = max(res,l)

    print(res)



# Generated by 1.1.4 https://github.com/kyuridenamida/atcoder-tools  (tips: You use the default template now. You can remove this line by using your custom template)
def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  # type: int
    S = next(tokens)  # type: str
    solve(N, S)

if __name__ == '__main__':
    main()

Buggy python submission (verdict: Time Limit Exceeded):
#!/usr/bin/env python3
import sys
import collections


def solve(N: int, S: str):

    dp = collections.defaultdict(set)
    for i,s in enumerate(S):
        for k,v in list(dp.items()):
            for vv in v:
                if vv + len(k) == i:
                    dp[k+s].add(vv)
        dp[s].add(i)
    
    dp_sorted = sorted(((k,v) for k,v in dp.items() if len(v) > 1),key=lambda x:len(x[0]),reverse=True)

    for k,v in dp_sorted:
        if max(v) - min(v) >= len(k):
            print(len(k))
            return

    print(0)

# Generated by 1.1.4 https://github.com/kyuridenamida/atcoder-tools  (tips: You use the default template now. You can remove this line by using your custom template)
def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  # type: int
    S = next(tokens)  # type: str
    solve(N, S)

if __name__ == '__main__':
    main()


Fixed submission:
#!/usr/bin/env python3
import sys
import collections
import itertools


def solve(N: int, S: str):
    dp = [[0 for _ in range(N)] for _ in range(N)]

    for i in range(N):
        if S[i] == S[-1]:
            dp[i][N-1] = 1

    res = 0
    for i in range(N-2,-1,-1):
        for j in range(N-2,i,-1):
            if S[i] == S[j]:
                dp[i][j] = dp[i+1][j+1] + 1
                l = dp[i][j]
                if j >= i+l:
                    res = max(res,l)

    print(res)



# Generated by 1.1.4 https://github.com/kyuridenamida/atcoder-tools  (tips: You use the default template now. You can remove this line by using your custom template)
def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  # type: int
    S = next(tokens)  # type: str
    solve(N, S)

if __name__ == '__main__':
    main()