Description
A good meal is a meal that contains exactly two different food items with a sum of deliciousness equal to a power of two.
You can pick any two different foods to make a good meal.
Given an array of integers deliciousness
where deliciousness[i]
is the deliciousness of the iββββββthββββ
ββββ item of food, return the number of different good meals you can make from this list modulo 109 + 7
.
Note that items with different indices are considered different even if they have the same deliciousness value.
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Example 1:
Input: deliciousness = [1,3,5,7,9] Output: 4 Explanation: The good meals are (1,3), (1,7), (3,5) and, (7,9). Their respective sums are 4, 8, 8, and 16, all of which are powers of 2.
Example 2:
Input: deliciousness = [1,1,1,3,3,3,7] Output: 15 Explanation: The good meals are (1,1) with 3 ways, (1,3) with 9 ways, and (1,7) with 3 ways.
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Constraints:
1 <= deliciousness.length <= 105
0 <= deliciousness[i] <= 220
Solution
Python3
class Solution:
def countPairs(self, A: List[int]) -> int:
M = 10 ** 9 + 7
res = 0
mp = Counter(A)
for i in range(22):
p = 1 << i
for v in mp:
target = p - v
if v == target:
res += mp[v] * (mp[v]-1)
else:
res += mp[v] * mp[target]
res //= 2
return res % M