
Problem Statement
In this problem, we are provided with an integer array nums
. The main objective is to make all elements in the array equal using a specified operation. This operation consists of several steps:
- Identify the largest value in the array, note both its value (
largest
) and its index (i
). In cases where multiple instances of this value exist, the one with the smallest index should be selected. - Find the second largest value (
nextLargest
) that is strictly smaller than thelargest
. - Replace the
largest
value at indexi
in the array withnextLargest
.
Our goal is to determine the minimum number of such operations required to equalize all elements in the array.
Examples
Example 1
Input:
nums = [5,1,3]
Output:
3
Explanation:
It takes 3 operations to make all elements in nums equal: 1. largest = 5 at index 0. nextLargest = 3. Reduce nums[0] to 3. nums = [3,1,3]. 2. largest = 3 at index 0. nextLargest = 1. Reduce nums[0] to 1. nums = [1,1,3]. 3. largest = 3 at index 2. nextLargest = 1. Reduce nums[2] to 1. nums = [1,1,1].
Example 2
Input:
nums = [1,1,1]
Output:
0
Explanation:
All elements in nums are already equal.
Example 3
Input:
nums = [1,1,2,2,3]
Output:
4
Explanation:
It takes 4 operations to make all elements in nums equal: 1. largest = 3 at index 4. nextLargest = 2. Reduce nums[4] to 2. nums = [1,1,2,2,2]. 2. largest = 2 at index 2. nextLargest = 1. Reduce nums[2] to 1. nums = [1,1,1,2,2]. 3. largest = 2 at index 3. nextLargest = 1. Reduce nums[3] to 1. nums = [1,1,1,1,2]. 4. largest = 2 at index 4. nextLargest = 1. Reduce nums[4] to 1. nums = [1,1,1,1,1].
Constraints
1 <= nums.length <= 5 * 104
1 <= nums[i] <= 5 * 104
Approach and Intuition
To better understand the task, let's go through the process using provided examples and constraints:
- The array size can vary considerably (has up to 50,000 elements), and each element's value is also substantial (up to 50,000). It’s crucial to consider efficient solutions due to these large potential sizes.
Example walkthroughs to clarify the process:
Simple case: Unequal elements
- Consider
nums = [5,1,3]
. - Find the largest (5 at index 0) and the next largest (3), so we adjust
nums[0]
to 3. This updates the array to[3,1,3]
. - Now, find the new largest (3 at index 0) and next largest (1), then adjust
nums[0]
to 1, updating the array to[1,1,3]
. - Finally, the largest (3 at index 2) is again reduced to the next largest (1), resulting in all elements being equal
[1,1,1]
. - All of this takes three operations, thus for input
[5,1,3]
, the process requires three operations to make all elements equal.
- Consider
Already equal elements
- When all elements are already equal, e.g.,
nums = [1,1,1]
, no operations are needed. Hence, the operation count is zero.
- When all elements are already equal, e.g.,
Repeated and distinct values
- For
nums = [1,1,2,2,3]
, the largest distinct value reduction sequence goes from 3 to 2 to 1. - Each step involves reducing the current highest value to the next highest unequal value until the entire array becomes homogeneous. This example demonstrates operations on cases where some numbers might already be equal, affecting the count of total operations and the intermediary operations for reaching the final uniform array state.
- For
Given the problem's constraints, a pivotal approach includes iterating to find the maximum, then the next largest value, and adjusting the array correspondingly. Keeping track of the number of operations and distinct numbers during the processing will aid in optimizing and determining when all elements have become equal.
Solutions
- C++
- Java
- Python
class Solution {
public:
int reduceNums(vector<int>& elements) {
sort(elements.begin(), elements.end());
int total_steps = 0;
int increment = 0;
for (int i = 1; i < elements.size(); i++) {
if (elements[i] != elements[i - 1]) {
increment++;
}
total_steps += increment;
}
return total_steps;
}
};
The provided C++ solution focuses on the problem of reducing the number of operations required to make all elements in an array equal. The approach includes sorting the array and then iterating through it to count the necessary reduction operations. Here's a concise explanation of how the solution works:
- Sort the array so that similar elements are adjacent. This step makes it easier to count unique elements and measure steps needed for each unique element to match the smallest element.
- Initialize two counters:
total_steps
to store the cumulative number of operations, andincrement
to track steps needed for consecutive unique elements. - Traverse the sorted array starting from the second element. For each unique element encountered (different from the previous element), increase the
increment
. Add the current value ofincrement
tototal_steps
. - By the end of the loop,
total_steps
will hold the total number of operations needed to make all array elements equal.
Make sure the elements
parameter passed to the reduceNums
function is non-empty to avoid any boundary errors. The function reduceNums
returns an integer representing the total reduction operations required.
class Solution {
public int reduceSteps(int[] numArray) {
Arrays.sort(numArray);
int result = 0;
int stepIncrement = 0;
for (int index = 1; index < numArray.length; index++) {
if (numArray[index] != numArray[index - 1]) {
stepIncrement++;
}
result += stepIncrement;
}
return result;
}
}
This Java solution tackles the problem of determining the minimal number of reduction operations needed to make all elements of an array equal. Each operation involves reducing any element of the array to any other smaller element.
Here's an overview of the approach used:
- First, sort the array in ascending order. This facilitates the comparison of each element with its predecessor.
- Initialize a counter
result
to track the total number of operations required, andstepIncrement
to count the number of distinct elements processed. - Iterate through the sorted array starting from the second element:
- When encountering a distinct element (i.e., a value change compared to the previous element), increment
stepIncrement
. - Add
stepIncrement
toresult
with each iteration over the array.
- When encountering a distinct element (i.e., a value change compared to the previous element), increment
- After looping through the entire array, return
result
which captures the count of all necessary reduction operations.
This approach ensures an efficient computation of steps by sorting the elements and calculating incremental moments where a decrement in distinct elements occurs.
class Solution:
def reduceOps(self, values: List[int]) -> int:
values.sort()
counter = 0
increment = 0
for index in range(1, len(values)):
if values[index] != values[index - 1]:
increment += 1
counter += increment
return counter
The Python3 implementation provided is designed to count the minimum number of operations required to make all elements in an array the same. Here's a breakdown of how the solution works:
- The input list
values
is first sorted. Sorting is crucial as it groups identical elements together and allows for sequential comparison. - Two variables are used:
counter
for tracking the number of operations, andincrement
for counting how many different previous elements have been encountered. - The function loops through the sorted list, starting from the second element. For each element, it checks if it is different from the element before it:
- If it is, the
increment
variable is increased, indicating that a new distinct value has been found. - The value of
increment
(which represents the accumulative number of unique previous elements) is then added tocounter
.
- If it is, the
- The total in
counter
at the end of the loop is returned, representing the total number of reduction operations needed.
This implementation effectively uses sorting and a single pass through the list, making it efficient in terms of both time and space complexity for the task of equalizing array elements through minimal operations.
No comments yet.