0NXGTs - Online C++ Compiler & Debugging Tool

#include<bits/stdc++.h>
using namespace std;

int main(){
	int n;
	cin>>n;

	vector<int> arr(n,0);

	for(int i = 0;i<n;i++){
		cin>>arr[i];
	}


	vector<int> projarr(n + 1,  0);

	for(int i = 1;i<n;i++){
		if(arr[i] < arr[i-1]){
			projarr[i] = arr[i-1] - arr[i];
			arr[i] = arr[i-1];
		}else{
			projarr[i] = 0;
		}
	}

	int ans = 0;
	int prev = 0;
	for(int i = 0; i < n; i++){
	    if(projarr[i] > prev){
	        ans += projarr[i] - prev;
	    }
	    prev = projarr[i];
	}

	cout<<ans<<endl;

	return 0;
}