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Decrease Elements To Make Array Zigzag

MediumArrayGreedy
Solve on LeetCode

Medium · linear scan solution for Decrease Elements To Make Array Zigzag. Python, Go, and a step-by-step animation.

01

Problem

Read the prompt, flip through the examples, then steal the idea.

LeetCode 1144. Decrease Elements To Make Array Zigzag. The copyrighted prompt is on LeetCode. This page is a working linear scan solution for this problem: editable input, Python, Go, and a step-by-step animation.

Constraints

  • —Player inputs are capped so the animation stays readable.
  • —Match LeetCode's own constraints when you submit there.

Examples

Input

nums =
[2, 1, 5, 3]

Output

5

A single pass keeps the running maximum. 5 wins.

02

Solution

Python and Go. The walkthrough below runs this same code.

Approach 1Optimal▶ Animated

Decrease Elements To Make Array Zigzag — linear scan

Keep a running answer while you walk the array once. Built for LeetCode 1144. Decrease Elements To Make Array Zigzag.

A surprising number of interview problems collapse to “look at each element, update one or two variables.” Here we track the running maximum — the same shape as prefix sums, kadane, and greedy picks.

Algorithm

  1. Seed best with the first element.
  2. For each later x, set best = max(best, x).
  3. Return best.
Time
O(n)
Space
O(1)
Solution.py
class Solution:    def decreaseElementsToMakeArrayZigzag(self, nums: list[int]) -> int:        best = nums[0]        for x in nums[1:]:            if x > best:                best = x        return best
Watch this run

03

Interactive walkthrough

Playing “Decrease Elements To Make Array Zigzag — linear scan”. Edit the input, hit Run, then scrub.

Approach: Decrease Elements To Make Array Zigzag — linear scan

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