1526. Minimum Number of Increments on Subarrays to Form a Target Array

https://leetcode.com/problems/minimum-number-of-increments-on-subarrays-to-form-a-target-array

Description

Given an array of positive integers target and an array initial of same size with all zeros.

Return the minimum number of operations to form a target array from initial if you are allowed to do the following operation:

• Choose any subarray from initial and increment each value by one.

The answer is guaranteed to fit within the range of a 32-bit signed integer. Example 1:

**Input:** target = [1,2,3,2,1]
**Output:** 3
**Explanation:** We need at least 3 operations to form the target array from the initial array.
[0,0,0,0,0] increment 1 from index 0 to 4 (inclusive).
[1,1,1,1,1] increment 1 from index 1 to 3 (inclusive).
[1,2,2,2,1] increment 1 at index 2.
[1,2,3,2,1] target array is formed.

Example 2:

**Input:** target = [3,1,1,2]
**Output:** 4
**Explanation:** (initial)[0,0,0,0] -> [1,1,1,1] -> [1,1,1,2] -> [2,1,1,2] -> [3,1,1,2] (target).

Example 3:

**Input:** target = [3,1,5,4,2]
**Output:** 7
**Explanation:** (initial)[0,0,0,0,0] -> [1,1,1,1,1] -> [2,1,1,1,1] -> [3,1,1,1,1] 
                                  -> [3,1,2,2,2] -> [3,1,3,3,2] -> [3,1,4,4,2] -> [3,1,5,4,2] (target).

Example 4:

**Input:** target = [1,1,1,1]
**Output:** 1

Constraints:

• 1 <= target.length <= 10^5

• 1 <= target[i] <= 10^5

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