package _interview_question
/**
* https://leetcode.com/discuss/interview-question/275785/facebook-phone-screen-count-subsets
*
* Input:
Given an array A of
-positive
-sorted
-no duplicate
-integer
A positive integer k
Output:
Count of all such subsets of A,
Such that for any such subset S,
Min(S) + Max(S) = k
subset should contain atleast two elements
input: {1,2,3,4,5}
* */
class Solution {
private val map = HashMap<Int, Int>()
private var result = 0.0
fun subSetMinMaxEqualK(nums: IntArray, k: Int):Int {
//1.backtracking, Time complexity: O(2^n), Space complexity:O(n)
//dfs(0, nums, ArrayList<Int>(), k)
//2.use map, just like 2 sum
//Time complexity: O(nlogn), Space complexity:O(n)
nums.sort()
for (i in nums.indices) {
val needFind = k - nums[i]
if (map.containsKey(needFind)) {
val value = i-map.get(needFind)!!-1
//1,2,3,4,5; k = 5, {1 4} there are 4 cases 2^2
result += Math.pow(2.0,value.toDouble())
}
map.put(nums[i], i)
}
return result.toInt()
}
private fun dfs(n: Int, nums: IntArray, cur: ArrayList<Int>, target: Int) {
val temp = ArrayList<Int>(cur)
val min = temp.min() ?: 0
val max = temp.max() ?: 0
val value = min + max
if (value == target) {
result++
}
for (i in n until nums.size) {
cur.add(nums[i])
dfs(i + 1, nums, cur, target)
cur.removeAt(cur.size - 1)
}
}
}
