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 ith item of food, return the number of different good meals you can make from this list modulo109 + 7.
Note that items with different indices are considered different even if they have the same deliciousness value.
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.
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.
1 <= deliciousness.length <= 1050 <= deliciousness[i] <= 220
use std::collections::HashMap;implSolution{pubfncount_pairs(deliciousness:Vec<i32>) -> i32{letmut count = HashMap::new();letmut ret = 0_i64;for i in0..deliciousness.len(){ count .entry(deliciousness[i]).and_modify(|c| *c += 1).or_insert(1);}for(&food0, c)in count.iter(){for i in0..22{let food1 = (1 << i) - food0;if food1 < food0 { ret = (ret + c * count.get(&food1).unwrap_or(&0)) % 1_000_000_007;}elseif food1 == food0 { ret = (ret + c *(c - 1) / 2) % 1_000_000_007;}else{break;}}} ret asi32}}