如何找到加起来等于给定总和的索引和组合？

Question

如何找到加起来等于给定总和的组合和相应的索引？而且，是否可以处理大小为500000（较大大小）的元素的列表？

输入：

l1 = [9,1, 2, 7, 6, 1, 5] 
target = 8

**Constraints**
1<=(len(l1))<=500000
1<=each_list_element<=1000

输出：

Format : {index:element}
{1:1, 5:1, 4:6}   #Indices : 1,5,4   Elements : 1,1,6
{1:1, 2:2,  6:5}
{5:1, 2:2,  6:5}
{1:1,  3:7}
{5:1,  3:7}
{2:2,  4:6}

已尝试：

from itertools import combinations

def test(l1, target):
    l2 = []
    l3 = []    
    if len(l1) > 0:
        for r in range(0,len(l1)+1):        
            l2 += list(combinations(l1, r))

        for i in l2:        
            if sum(i) == target:
                l3.append(i)

    return l3

l1 = [9,1, 2, 7, 6, 1, 5] 
target = 8
print(test(l1,target))

[(1, 7), (2, 6), (7, 1), (1, 2, 5), (1, 6, 1), (2, 1, 5)]

有人可以引导我吗？

UPDATE

Apart from above, code fails to handle these scenarios
Input = [4,6,8,5,3]
target = 3

Outputs {} , need to output {4:3}

Input = [4,6,8,3,5,3]
target = 3

Outputs {} , need to output {5:3,3:3}   #corrected index

Input = [1,2,3,15]
target = 15

Outputs = {}, need to output {3:15}

Answer 1

您的代码很接近，我将使用枚举以元组对的形式获取索引和值。我总是删除任何索引和值元组，其中该值大于目标值，因为这不可能匹配。这将产生较少的组合。然后像您一样，我只遍历元组的排列并对每个排列中的值求和，如果它求和到目标，则产生该排列。最后在循环中输出值，我将烫发给dict转换为想要的dict格式

from itertools import combinations


def find_sum_with_index(l1, target):
    index_vals = [iv for iv in enumerate(l1) if iv[1] < target]
    for r in range(1, len(index_vals) + 1):
        for perm in combinations(index_vals, r):
            if sum([p[1] for p in perm]) == target:
                yield perm


l1 = [9, 1, 2, 7, 6, 1, 5]
target = 8
for match in find_sum_with_index(l1, target):
    print(dict(match))

输出

{1: 1, 3: 7}
{2: 2, 4: 6}
{3: 7, 5: 1}
{1: 1, 2: 2, 6: 5}
{1: 1, 4: 6, 5: 1}
{2: 2, 5: 1, 6: 5}

Answer 2

您可以仅使用索引函数来获取索引，并在字典的帮助下将它们存储为键：值对，位于另一个列表中，如下所示，

from itertools import combinations

def test(l1, target):
    l2 = []
    l3 = []
    l4=[]
    dict1={}
    a=0
    if len(l1) > 0:
        for r in range(0,len(l1)+1):        
            l2 += list(combinations(l1, r))

        for i in l2:
            dict1={}
            if sum(i) == target:

                for j in i:
                    a=l1.index(j)
                    dict1[a]=j
                l4.append(dict1)
                l3.append(i)

    return l4

l1 = [4,6,8,5,3]
target = 3

print(test(l1,target))

输出：

[{4: 3}]

如您所见，l1 = [4,6,8,5,3] target = 3的条件以前不起作用。

希望这会有所帮助！