python - 在 python 中查找对称对

Question

我有以下代码可以从给定的输入中查找并打印所有对称对。

'''
 Given a list of number pairs.
 If pair(i,j) exist, and pair(j,i) exist report all such pairs.
'''

def find_all_symmetric_pairs(inp_dic):

    for key in inp_dic:
        val = inp_dic[key]

        if inp_dic[val] == key:
            return key,val
    return -1,-1


inp_dic = {'1':'3','2':'6','3':'5','7':'4','5':'3','8':'7'}

print type(inp_dic)
key,value = find_all_symmetric_pairs(inp_dic)

print "key:"+str(key)
print "value:"+str(value)

输出:

 key:3
 value:5

但是如果我将输入更改为

inp_dic = {(1,3),(2,6),(3,5),(7,4),(5,3),(8,7)}

或

inp_dic = {{1,3},{2,6},{3,5},{7,4},{5,3},{8,7}}

我很难迭代。我如何实现相同的目标？

Answer 1

这似乎是一个有用的解决方案:

d = {'1':'3','2':'6','3':'5','7':'4','5':'3','8':'7'}
pairs = [(key, value) for key, value in d.items()]
answer = [(x, y) for (x, y) in pairs if (y, x) in pairs]
print(answer)

输出

[('3', '5'), ('5', '3')]

如果我们将 pairs 设为 set 而不是 list 也可能会更快:

d = {'1':'3','2':'6','3':'5','7':'4','5':'3','8':'7'}
pairs = {(key, value) for key, value in d.items()}
answer = [(x, y) for (x, y) in pairs if (y, x) in pairs]
print(answer)

输出

[('3', '5'), ('5', '3')]