786. K-th Smallest Prime Fraction

A sorted list A contains 1, plus some number of primes. Then, for every p < q in the list, we consider the fraction p/q.

What is the K-th smallest fraction considered? Return your answer as an array of ints, where answer[0] = p and answer[1] = q.

**Examples:**
Input: A = [1, 2, 3, 5], K = 3
Output: [2, 5]
Explanation:
The fractions to be considered in sorted order are:
1/5, 1/3, 2/5, 1/2, 3/5, 2/3.
The third fraction is 2/5.

Input: A = [1, 7], K = 1
Output: [1, 7]

Note:

• A will have length between 2 and 2000.
• Each A[i] will be between 1 and 30000.
• K will be between 1 and A.length * (A.length - 1) / 2.

# @lc code=start
using LeetCode

function kth_smallest_prime_fraction(arr::Vector{Int}, k::Int)
    hp = BinaryMinHeap(1 .// arr[2:end])
    next_prime = Dict((arr[i], arr[i+1]) for i in 1:length(arr)-1)
    while (k -= 1) > 0
        tp = pop!(hp)
        if next_prime[tp.num] < tp.den
            push!(hp, next_prime[tp.num] // tp.den)
        end
    end
    return first(hp)
end
# @lc code=end

kth_smallest_prime_fraction (generic function with 1 method)

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