ruozhi.py

# Uses python3
import sys
from collections import namedtuple

Segment = namedtuple('Segment', 'start end')


def optimal_points(segments):
    points = []
    segments_by_end = sorted(segments, key=lambda x: x.end)
    segments_by_start = sorted(segments, key=lambda x: x.start)

    while len(segments_by_end) > 0:
        seg = segments_by_end[0]
        i = 0
        # Loop through all points in segments_by_start
        # if the start point is on the left (or equal)
        # remove it from both list
        while i < len(segments_by_start):
            if segments_by_start[i].start <= seg.end:
                segments_by_end.remove(segments_by_start[i])  # remove it from this list first
                segments_by_start.remove(segments_by_start[i])
            else:
                i += 1
        points.append(seg.end)

    return list(set(points))


if __name__ == '__main__':
    input = sys.stdin.read()
    n, *data = map(int, input.split())
    segments = list(map(lambda x: Segment(x[0], x[1]), zip(data[::2], data[1::2])))
    points = optimal_points(segments)
    print(len(points))
    for p in points:
        print(p, end=' ')


Input
3
1 3
2 5
3 6

Ouput
1
3
        
        
Input        
4
4 7
1 3
2 5
5 6

Output
2
3 6