백준 15649번 N과 M

import sys

input = sys.stdin.readline

n, m = map(int, input().split())

selected = [0] * (m)


def solve(x):
    if x == m + 1:
        for s in selected:
            print(s, end=' ')
        print()
    else:
        for candidate in range(1, n + 1):
            used = False
            for idx in range(x):
                if candidate == selected[idx]:
                    used = True
            if not used:
                selected[x - 1] = candidate
                solve(x + 1)
                selected[x - 1] = 0


solve(1)

import sys
n, m = map(int, sys.stdin.readline().split(' '))

selected = [0 for _ in range(m)]
used = [0 for _ in range(n + 1)]
def rec_func(k):
    if k == m:
        for x in selected:
            sys.stdout.write(str(x) + ' ')
        sys.stdout.write('\n')
    else:
        for cand in range(1, n + 1):
            # used 배열로 시간 복잡도 줄이기
            if used[cand]:
                continue
            selected[k] = cand
            used[cand] = 1
            rec_func(k + 1)
            selected[k] = 0
            # 실수하기 쉬운 부분, 재귀호출 후에 초기화해줘야 함
            used[cand] = 0

rec_func(0)