Znuzcs - Online C++0x Compiler & Debugging Tool

#include <bits/stdc++.h>
using namespace std;
#define ll long long int
const int M = 1e9 + 7;

const int N = 2e5 + 10;

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    int n;
    cin >> n;
    vector<int> v(n);
    for (int i = 0; i < n; i++)
        cin >> v[i];
    vector<int> proj(n);
    int ma = 0;
    for (int i = 0; i < n; i++)
    {
        ma = max(ma, v[i]);
        proj[i] = ma - v[i];
    }
    int i = 1;
    int ans = 0;
    while (i < n)
    {
        while (i < n && proj[i - 1] <= proj[i])
            i++;
        ans += proj[i - 1];
        while (i < n && proj[i - 1] >= proj[i])
            i++;
    }

    cout << ans << endl;
    return 0;
}