3914. Minimum Operations to Make Array Non Decreasing

You are given an integer array nums of length n.

In one operation, you may choose any subarray 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.

class Solution {
public:
    long long minOperations(vector<int>& nums) {
        long long res = 0, prv = 0, pre = 0;
        for(auto& n : nums) {
            if(n + pre < prv) {
                int diff = prv - (n + pre);
                pre += diff;
                res += diff;
            }
            prv = n + pre;
        }
        return res;
    }
};