为什么不附加第一个元素

Question

I am trying to print all subsets for the subset sum problem. That is, print all subsets from an array which sum to a given number. However, in the later occurrences, the subsets seem to omit the first one or two entries from the final answer, why is that??

import numpy as np
def calcSubsets(arr, i, target, current, dp):
    if(i==0 and target != 0 and dp[0][target]):
        current.append(arr[i])
        print(current)
        current.clear()
        return
    if(i==0 and target ==0):
        print(current)
        current.clear() 
        return
    if(dp[i-1][target]):
        temp = []
        temp = current
        calcSubsets(arr, i-1, target, temp, dp)
    if(target >= arr[i] and dp[i-1][target-arr[i]]):
        current.append(arr[i])
        calcSubsets(arr,i-1,target-arr[i], current, dp)


def printAll(arr, n, target):
    if(n==0 or target<0):
        return
#    for i in range(0,n):
#        dp[i][0] = True
    for i in dp:
        i[0] = True
        i[1:] = False
    if(arr[0]<=target):
        dp[0][arr[0]] = True
    for i in range(1,n):
        for j in range(0,target+1):
            dp[i][j] = (dp[i-1][j] or dp[i-1][j-arr[i]]) if (arr[i] <= j) else dp[i-1][j]

    if(not(dp[n-1][target])):
        print("INFEASIBLE")
        return

    current = []
    calcSubsets(arr,n-1,target, current, dp)

#arr = fa.toArray('purple.txt')
arr = [1,2,3,4,5,6]
target = 15
n = len(arr)
dp = np.empty((n,target+1), dtype=bool)
printAll(arr, n, target)


Expected output

[5,4,3,2,1]
[6,4,3,2]
[6,5,3,1]
[6,5,4]

Actual Output

[5,4,3,2,1]
[6,4,3,2]
[5,3,1]
[6,5,4]

Please help.

Answer 1

I suggest complete rewrite of the code, with use of itertools :

# first we grab powerset() from 
# https://docs.python.org/3/library/itertools.html#itertools-recipes
from itertools import chain, combinations
def powerset(iterable):
    "powerset([1,2,3]) --> () (1,) (2,) (3,) (1,2) (1,3) (2,3) (1,2,3)"
    s = list(iterable)
    return chain.from_iterable(combinations(s, r) for r in range(len(s)+1))

arr = [1,2,3,4,5,6]
target = 15
# now we filter out subsets with wrong sum
for t in powerset(arr):
    if sum(t) == target:
        print(t)

That's all.