Problem:
Let's arrange a deck of cards. There are totally 36 cards of 4 suits(S, H, C, D) and 9 values (1, 2, ... 9). For example, 'eight of heart' is represented by H8 and 'one of diamonds' is represented by D1.  Your task is to write a program which sorts a given set of cards in ascending order by their values using the Bubble Sort algorithms and the Selection Sort algorithm respectively. These algorithms should be based on the following pseudocode:                 BubbleSort(C) 1 for i = 0 to C.length-1 2     for j = C.length-1 downto i+1 3         if C[j].value < C[j-1].value 4             swap C[j] and C[j-1]                 SelectionSort(C) 1 for i = 0 to C.length-1 2     mini = i 3     for j = i to C.length-1 4         if C[j].value < C[mini].value 5             mini = j 6     swap C[i] and C[mini]   Note that, indices for array elements are based on 0-origin.  For each algorithm, report the stability of the output for the given input (instance). Here, 'stability of the output' means that: cards with the same value appear in the output in the same order as they do in the input (instance).

Incorrect submission (verdict: Wrong Answer):
class Card:
    def __init__(self, mark, value):
        self.mark = mark
        self.value = value

    def __eq__(self, other):
        return self.value == other.value and self.mark == self.mark

    def __lt__(self, other):
        return self.value < other.value

    def __str__(self):
        return self.mark + str(self.value)


def BubbleSort(arr):
    res = arr.copy()
    swap_flg = True
    i = 0
    while swap_flg:
        swap_flg = False
        for j in range(len(res) - 1, i, -1):
            if (res[j] < res[j - 1]):
                res[j], res[j - 1] = res[j - 1], res[j]
                swap_flg = True
        i += 1
    return res


def SelectionSort(arr):
    res = arr.copy()
    for i in range(0, len(res)):
        minj = i
        for j in range(i, N):
            if res[j] < res[minj]:
                minj = j
        if (i != minj):
            res[i], res[minj] = res[minj], res[i]
    return res


def isStable(in_arr, out_arr):
    stable_arr = BubbleSort(in_arr)
    return all(out_arr[i] == stable_arr[i] for i in range(0, len(out_arr)))


N = int(input())
arr = [Card(s[0], int(s[1])) for s in input().split()]
b_arr = BubbleSort(arr)
print(' '.join(map(str, b_arr)))
print('Stable' if isStable(arr, b_arr) else 'Not stable')
s_arr = SelectionSort(arr)
print(' '.join(map(str, s_arr)))
print('Stable' if isStable(arr, s_arr) else 'Not stable')



Fixed, accepted submission:
class Card:
    def __init__(self, mark, value):
        self.mark = mark
        self.value = value

    def __eq__(self, other):
        if not isinstance(other, Card):
            return NotImplemented
        return self.value == other.value and self.mark == other.mark

    def __lt__(self, other):
        return self.value < other.value

    def __str__(self):
        return self.mark + str(self.value)


def BubbleSort(arr):
    res = [Card(c.mark, c.value) for c in arr]
    swap_flg = True
    i = 0
    while swap_flg:
        swap_flg = False
        for j in range(len(res) - 1, i, -1):
            if (res[j] < res[j - 1]):
                res[j], res[j - 1] = res[j - 1], res[j]
                swap_flg = True
        i += 1
    return res


def SelectionSort(arr):
    res = [Card(c.mark, c.value) for c in arr]
    for i in range(0, len(res)):
        minj = i
        for j in range(i, N):
            if res[j] < res[minj]:
                minj = j
        if (i != minj):
            res[i], res[minj] = res[minj], res[i]
    return res


def isStable(in_arr, out_arr):
    stable_arr = BubbleSort(in_arr)
    return all(out_arr[i] == stable_arr[i] for i in range(0, len(out_arr)))


N = int(input())
arr = [Card(s[0], int(s[1])) for s in input().split()]
b_arr = BubbleSort(arr)
print(' '.join(map(str, b_arr)))
print('Stable' if isStable(arr, b_arr) else 'Not stable')
s_arr = SelectionSort(arr)
print(' '.join(map(str, s_arr)))
print('Stable' if isStable(arr, s_arr) else 'Not stable')