Is Merge Operations to Turn Array Into a Palindrome easy or hard?

The problem is generally classified as Medium. The challenge is recognizing that merging the smaller side greedily leads to the optimal result. Once the two-pointer insight is clear, the implementation becomes straightforward.

Merge Operations to Turn Array Into a Palindrome Python/Java solution

Most implementations follow the same greedy logic regardless of language. Maintain two indices at the ends of the array, compare values, and merge the smaller side by adding the adjacent element. This approach works consistently in Python, Java, C++, and Go with O(n) time and constant space.

How to solve Merge Operations to Turn Array Into a Palindrome in O(n)?

Use two pointers starting from the left and right ends. If both values match, move the pointers inward. If the left value is smaller, merge it with the next element and increment the left pointer. If the right value is smaller, merge it with the previous element and decrement the right pointer. Each step moves a pointer inward, producing linear time complexity.

What is the best approach for Merge Operations to Turn Array Into a Palindrome?

The optimal approach uses a greedy two-pointer strategy. Start pointers at both ends of the array and compare values. When they differ, merge the smaller side with its adjacent element so its sum grows toward the opposite value. This guarantees the minimum number of merges and runs in O(n) time with O(1) space.

Is Merge Operations to Turn Array Into a Palindrome asked at Google/Amazon/Meta?

Palindrome transformation and two-pointer greedy problems appear frequently in interviews at companies like Amazon, Google, and Meta. While this exact problem may vary in wording, the pattern of comparing symmetric elements and merging or adjusting values is a common interview theme.

What data structure is used in Merge Operations to Turn Array Into a Palindrome?

The problem primarily uses arrays with a two-pointer traversal technique. No additional data structures such as hash maps or stacks are required. The algorithm modifies or accumulates values directly in the array while scanning from both ends.

What is the time complexity of Merge Operations to Turn Array Into a Palindrome?

The optimal greedy two-pointer solution runs in O(n) time because each element is processed at most once as the pointers move inward. Space complexity is O(1) since the algorithm only uses a few variables and does not allocate extra data structures.

Description Hints 3 Solution Video 5:59

2422. Merge Operations to Turn Array Into a Palindrome

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You are given an array nums consisting of positive integers.

You can perform the following operation on the array any number of times:

Choose any two adjacent elements and replace them with their sum.
- For example, if nums = [1,2,3,1], you can apply one operation to make it [1,5,1].

Return the minimum number of operations needed to turn the array into a palindrome.

Example 1:

Input: nums = [4,3,2,1,2,3,1]
Output: 2
Explanation: We can turn the array into a palindrome in 2 operations as follows:
- Apply the operation on the fourth and fifth element of the array, nums becomes equal to [4,3,2,3,3,1].
- Apply the operation on the fifth and sixth element of the array, nums becomes equal to [4,3,2,3,4].
The array [4,3,2,3,4] is a palindrome.
It can be shown that 2 is the minimum number of operations needed.

Example 2:

Input: nums = [1,2,3,4]
Output: 3
Explanation: We do the operation 3 times in any position, we obtain the array [10] at the end which is a palindrome.

Constraints:

1 <= nums.length <= 10⁵
1 <= nums[i] <= 10⁶

Asked at 5 companies

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Topics

Hints open one at a time

Hint 1

Can you find how many operations are needed to make the first element of the array equal to the last element?

Hint 2

Notice that you can use the same idea of the previous hint to make the second element equal to the second last one.

Hint 3

Use the same idea until all elements of the array are used.

5:59

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Starter codePython 3Spaces: 4

Examples

Case 1Case 2

Input

[4,3,2,1,2,3,1]

Input

[1,2,3,4]

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