3_N

Способ 1:

def merge_sort(array):
    if len(array) == 1:
        return array

    left = merge_sort(array[:len(array) // 2])
    right = merge_sort(array[len(array) // 2:])

    result = []
    l, r = 0, 0
    while l < len(left) and r < len(right):
        if left[l] <= right[r]:
            result.append(left[l])
            l += 1
        else:
            result.append(right[r])
            r += 1
    while l < len(left):
        result.append(left[l])
        l += 1
    while r < len(right):
        result.append(right[r])
        r += 1
    return result


n = int(input())
flowerbeds = []
for i in range(n):
    flowerbed = list(map(int, input().split()))
    flowerbeds.append(flowerbed)

flowerbeds = merge_sort(flowerbeds)

i_start = 0
i_end = 1
start = flowerbeds[0][i_start]
end = flowerbeds[0][i_end]

for i in range(n):
    if flowerbeds[i][i_start] >= start and flowerbeds[i][i_end] <= end:
        # start--------------------------end
        #        i_start----------i_end
        continue
    if flowerbeds[i][i_start] <= end:
        # start-------end
        #    i_start----------i_end
        end = flowerbeds[i][i_end]
    else:
        # start----end
        #                 i_start----i_end
        print(start, end)
        start = flowerbeds[i][i_start]
        end = flowerbeds[i][i_end]
print(start, end)

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Способ 2:

def merge_sort(array):
    if len(array) == 1:
        return array

    left = merge_sort(array[:len(array) // 2])
    right = merge_sort(array[len(array) // 2:])

    result = []
    l, r = 0, 0
    while l < len(left) and r < len(right):
        if left[l] <= right[r]:
            result.append(left[l])
            l += 1
        else:
            result.append(right[r])
            r += 1
    while l < len(left):
        result.append(left[l])
        l += 1
    while r < len(right):
        result.append(right[r])
        r += 1

    return result


n = int(input())
flowerbeds_starts = []
flowerbeds_ends = []
for pos in range(n):
    flowerbed = input().split()
    flowerbeds_starts.append(int(flowerbed[0]))
    flowerbeds_ends.append(int(flowerbed[1]))

flowerbeds_starts = merge_sort(flowerbeds_starts)
flowerbeds_ends = merge_sort(flowerbeds_ends)

start = flowerbeds_starts[0]
end = flowerbeds_ends[0]
for pos in range(1, n):
    if flowerbeds_ends[pos - 1] >= end:
        end = flowerbeds_ends[pos - 1]
    if flowerbeds_starts[pos] > flowerbeds_ends[pos - 1]:
        print(start, end)
        start = flowerbeds_starts[pos]
        end = flowerbeds_ends[pos]
end = flowerbeds_ends[n - 1]
print(start, end)