Primary school students Blue Bridge Cup Python breakthrough | combined output

Learn Python from the doll! Record the questions in the Blue Bridge Cup Python learning and test preparation process, and record every moment.

Attached is a summary post: Pupils Blue Bridge Cup Python Breakthrough | Summary_COCOgsta's Blog-CSDN Blog

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【Description】

Arrangement and combination are commonly used mathematical methods, where combination is to extract r elements from n elements (regardless of order and r≤n), we can simply understand n elements as natural numbers 1, 2,..., n, from which r numbers are chosen arbitrarily.

You are now asked to output all combinations.

For example n=5, r=3, all combinations are:

123,124,125,134,135,145,234,235,245,345.

【Enter description】

A row of two natural numbers n, r (1<n≤21, 0≤r≤n).

【Output description】

For all combinations, each combination occupies one line and its elements are arranged in ascending order, each element occupies a position of three characters, and all combinations are also in lexicographical order.

【Sample input】

5 3

【Sample output】

1 2 3

1 2 4

1 2 5

1 3 4

1 3 5

1 4 5

2 3 4

2 3 5

2 4 5

3 4 5

【Code Explanation】

n,r = [int(i) for i in input().split()]

arr = [0 for i in range(n+1)]



def dfs(x, start):
    if x > r:
        for i in range(1, r+1):
            print('   '+str(arr[i]), end='')
        print()
        return

    for i in range(start, n+1):
        arr[x] = i
        dfs(x+1, i+1)
        arr[x] = 0

dfs(1, 1)
复制代码

【operation result】

5 3
   1   2   3
   1   2   4
   1   2   5
   1   3   4
   1   3   5
   1   4   5
   2   3   4
   2   3   5
   2   4   5
   3   4   5