Question

2208. Minimum Operations to Halve Array Sum

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Description

You are given an array nums of positive integers. In one operation, you can choose any number from nums and reduce it to exactly half the number. (Note that you may choose this reduced number in future operations.)

Return_ the minimum number of operations to reduce the sum of _nums_ by at least half._

 

Example 1:

Input: nums = [5,19,8,1]
Output: 3
Explanation: The initial sum of nums is equal to 5 + 19 + 8 + 1 = 33.
The following is one of the ways to reduce the sum by at least half:
Pick the number 19 and reduce it to 9.5.
Pick the number 9.5 and reduce it to 4.75.
Pick the number 8 and reduce it to 4.
The final array is [5, 4.75, 4, 1] with a total sum of 5 + 4.75 + 4 + 1 = 14.75. 
The sum of nums has been reduced by 33 - 14.75 = 18.25, which is at least half of the initial sum, 18.25 >= 33/2 = 16.5.
Overall, 3 operations were used so we return 3.
It can be shown that we cannot reduce the sum by at least half in less than 3 operations.

Example 2:

Input: nums = [3,8,20]
Output: 3
Explanation: The initial sum of nums is equal to 3 + 8 + 20 = 31.
The following is one of the ways to reduce the sum by at least half:
Pick the number 20 and reduce it to 10.
Pick the number 10 and reduce it to 5.
Pick the number 3 and reduce it to 1.5.
The final array is [1.5, 8, 5] with a total sum of 1.5 + 8 + 5 = 14.5. 
The sum of nums has been reduced by 31 - 14.5 = 16.5, which is at least half of the initial sum, 16.5 >= 31/2 = 15.5.
Overall, 3 operations were used so we return 3.
It can be shown that we cannot reduce the sum by at least half in less than 3 operations.

 

Constraints:

• 1 <= nums.length <= 105
• 1 <= nums[i] <= 107

Solutions

Solution 1

class Solution:
  def halveArray(self, nums: List[int]) -> int:
    s = sum(nums) / 2
    h = []
    for v in nums:
      heappush(h, -v)
    ans = 0
    while s > 0:
      t = -heappop(h) / 2
      s -= t
      heappush(h, -t)
      ans += 1
    return ans

class Solution {
  public int halveArray(int[] nums) {
    double s = 0;
    PriorityQueue<Double> q = new PriorityQueue<>(Collections.reverseOrder());
    for (int v : nums) {
      q.offer(v * 1.0);
      s += v;
    }
    s /= 2.0;
    int ans = 0;
    while (s > 0) {
      double t = q.poll();
      s -= t / 2.0;
      q.offer(t / 2.0);
      ++ans;
    }
    return ans;
  }
}

class Solution {
public:
  int halveArray(vector<int>& nums) {
    priority_queue<double> q;
    double s = 0;
    for (int& v : nums) {
      s += v;
      q.push(v);
    }
    s /= 2.0;
    int ans = 0;
    while (s > 0) {
      double t = q.top() / 2;
      q.pop();
      s -= t;
      q.push(t);
      ++ans;
    }
    return ans;
  }
};

func halveArray(nums []int) (ans int) {
  var s float64
  q := hp{}
  for _, x := range nums {
    s += float64(x)
    heap.Push(&q, float64(x))
  }
  s /= 2
  for s > 0 {
    x := heap.Pop(&q).(float64)
    ans++
    s -= x / 2
    heap.Push(&q, x/2)
  }
  return
}

type hp struct{ sort.Float64Slice }

func (h hp) Less(i, j int) bool { return h.Float64Slice[i] > h.Float64Slice[j] }
func (h *hp) Push(v any)    { h.Float64Slice = append(h.Float64Slice, v.(float64)) }
func (h *hp) Pop() any {
  a := h.Float64Slice
  v := a[len(a)-1]
  h.Float64Slice = a[:len(a)-1]
  return v
}

function halveArray(nums: number[]): number {
  let s: number = nums.reduce((a, b) => a + b) / 2;
  const h = new MaxPriorityQueue();
  for (const v of nums) {
    h.enqueue(v, v);
  }
  let ans: number = 0;
  while (s > 0) {
    let { element: t } = h.dequeue();
    t /= 2;
    s -= t;
    h.enqueue(t, t);
    ans += 1;
  }
  return ans;
}

Solution 2

func halveArray(nums []int) (ans int) {
  half := 0
  for i := range nums {
    nums[i] <<= 20
    half += nums[i]
  }
  h := hp{nums}
  heap.Init(&h)
  for half >>= 1; half > 0; ans++ {
    half -= h.IntSlice[0] >> 1
    h.IntSlice[0] >>= 1
    heap.Fix(&h, 0)
  }
  return
}

type hp struct{ sort.IntSlice }

func (h hp) Less(i, j int) bool { return h.IntSlice[i] > h.IntSlice[j] }
func (hp) Push(any)       {}
func (hp) Pop() (_ any)     { return }