LeetCode-in-Java

3914. Minimum Operations to Make Array Non Decreasing

Medium

You are given an integer array nums of length n.

In one operation, you may choose any non-empty subarrays nums[l..r] and increase each element in that subarray by x, where x is any positive integer.

Return the minimum possible sum of the values of x across all operations required to make the array non-decreasing.

An array is non-decreasing if nums[i] <= nums[i + 1] for all 0 <= i < n - 1.

Example 1:

Input: nums = [3,3,2,1]

Output: 2

Explanation:

One optimal set of operations:

• Choose subarray [2..3] and add x = 1 resulting in [3, 3, 3, 2]
• Choose subarray [3..3] and add x = 1 resulting in [3, 3, 3, 3]

The array becomes non-decreasing, and the total sum of chosen x values is 1 + 1 = 2.

Example 2:

Input: nums = [5,1,2,3]

Output: 4

Explanation:

One optimal set of operations:

• Choose subarray [1..3] and add x = 4 resulting in [5, 5, 6, 7]

The array becomes non-decreasing, and the total sum of chosen x values is 4.

Constraints:

• 1 <= n == nums.length <= 105
• 1 <= nums[i] <= 109

Solution

public class Solution {
    public long minOperations(int[] nums) {
        int n = nums.length;
        long ans = 0;
        for (int i = 1; i < n; ++i) {
            ans += Math.max(nums[i - 1] - nums[i], 0);
        }
        return ans;
    }
}

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