比较两个列表的元素

Question

I have been given two lists, say list1 and list2. I have to arrange the elements of the list1 in such a way that at particular index the element of list1 is greater than the element of list2. We have to find how many such elements of list1 are there. For example:

list1=[20,30,50]
list2=[60,40,25]

Here only element index 2 is greater ie 50>25, but if we swap 50 and 30 in list1 So,

list1=[20,50,30]
list2=[60,40,25]

then 50 > 40 ( at index 1) and 30 > 25 (at index 2). So we got 2 elements 50 and 30 which are greater at their respective index. Here is my approach

def swap(a,b):
    a,b=b,a
    return a,b
n=3
g=list(map(int,input().split()))
o=list(map(int,input().split()))
c=0
for i in range(n):
    if o[i]>g[i]:
        for j in range(i+1,n):
            if g[j]>o[i]:
                g[i],g[j]=swap(g[i],g[j])
                c+=1
                break
    else:
        c+=1
print(c)

But for

list1= [3,6,7,5,3,5,6,2,9,1]
list2= [2,7,0,9,3,6,0,6,2,6]

Its giving c=6 but expected output is c=7

Answer 1

You have to sort the two lists and then run through them to find "matches" where a value of list1 is greater than the next value of list2. This will pair up the values with the smallest possible difference and thus maximize the pairings.

For example:

list1=[20,30,50]
list2=[60,40,25]

iter1 = iter(sorted(list1))  # iterator to run through sorted list1
n1    = next(iter1,None)     # n1 is current number in list1
count = 0                    # count of paired elements (n1>n2)
for n2 in sorted(list2):               # go through sorted list 2
    while n1 is not None and n1 <= n2: # skip over ineligible items of list1
        n1 = next(iter1,None)
    if n1 is None: break               # stop when list 1 is exhausted
    count += 1                         # count 1 pair and move on to next of list2

print(count) # 2

Answer 2

list1= [3,6,7,5,3,5,6,2,9,1]
list2= [2,7,0,9,3,6,0,6,2,6]

list1 = sorted(list1)
it = iter(enumerate(list1))
list2  = sorted(list2)
c = next(it)
good = []
for i, n in enumerate(list2 ):
    try:
        while c[1] < n:
            c = next(it)
        good.append([i, c[0]])
        c = next(it)
    except StopIteration:
        break

for idx1, idx2 in good:
    list1[idx1], list1[idx2] = list1[idx2], list1[idx1]

final_l1_l2 = sum(a > b for a, b in zip(list1, list2))# how many l1 are > l2
print(final_l1_l2)

output:

   7

also, you can print list1 and list2 after the rearrange:

print(list1)
print(list2)

output:

[1, 2, 3, 3, 5, 6, 6, 7, 9, 5]
[0, 0, 2, 2, 3, 6, 6, 6, 7, 9]

the idea is to sort both lists and then to check what elements from list1 are greater than the elements from list2 if one element from list1 it is smaller then the current element from list2 just go to the next element from the list1 till there are no more elements in list1