순열/가지치기

#back tracking
#처음에 2가 나오면 안되는 경우 만들기
n = int(input())
arr = [1,2,3,4,5,6]
path=['']*n
used=[0]*6
def abc(level):
    if path[0] == 2:
        return #back tracking
    if level == n:
        for i in range(n):
            print(path[i],end=' ')
        print()
        return

    for i in range(6):
        # if level == 0 and arr[i] == 2:
        #     continue
        path[level] = arr[i]
        abc(level+1)
        path[level]=0
abc(0)​

---

#back tracking
n = int(input())
arr = [1,2,3,4,5,6]
path=['']*n
used=[0]*6

def abc(level):
    if level>1 and (path[level-1]==path[level-2]):
        return
    
    if level == n:
        for i in range(n):
            print(path[i],end=' ')
        print()
        return

    for i in range(6):
        # if level>0 and (path[level-1]==arr[i]): #path[level-1] == 들어온곳, arr[i]== 들어갈 곳
        #     continue
        path[level] = arr[i]
        abc(level+1)

        path[level]=0
abc(0)

---

#진입을 아예 안하는 경우
n = int(input())
arr = [1,2,3,4,5,6]
path=['']*n
used=[0]*6

def abc(level):
    if level == n:
        for i in range(n):
            print(path[i],end=' ')
        print()
        return

    for i in range(6):
        if level == 0 and arr[i] == 2:
            continue
        path[level] = arr[i]
        abc(level+1)
        path[level]=0
abc(0)

---

#back tracking
#처음에 2가 나오면 안되는 경우 만들기
n = int(input())
arr = [1,2,3,4,5,6]
path=['']*n
used=[0]*6
def abc(level):
    if path[0] == 2:
        return #back tracking
    if level == n:
        for i in range(n):
            print(path[i],end=' ')
        print()
        return

    for i in range(6):
        # if level == 0 and arr[i] == 2:
        #     continue
        path[level] = arr[i]
        abc(level+1)
        path[level]=0
abc(0)