Buy Low, Sell High

#include <bits/stdc++.h>

#define ll long long
#define lll __int128
#define pii pair<int, int>
#define M 1000000007
#define N (1<<20)
using namespace std;

int t[N], z[N];

int main () {
	ll nn;
	cin>>nn;
	int c = 1e9;
	for(int i=1; i<=nn; ++i){
		int a; cin >> a;
		z[i] = a;
		t[i] = max(t[i-1], a-c);
		c = min(a, c);
	}
	int V = 0;
	c=0;
	for(int i=nn; i>=1; --i){
		c = max(c, z[i]);
		V = max(V, t[i]+c-z[i]);
	}
	cout << V;
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED