I,J [NOIP2013]积木大赛, [NOIP2018]道路铺设

直接上结论，对 数组差分以后所有正数或所有负数的绝对值即为答案。

my code:

#include <bits/stdc++.h>
using namespace std;
const int maxn = 1e5 + 10;
int n,ans;
int a[maxn];
int main(){
    scanf("%d",&n);
    for(int i = 1;i <= n;i++){
        scanf("%d",&a[i]);
        if(a[i] > a[i - 1]) ans += a[i] - a[i - 1];
    }
    printf("%d",ans);
    return 0;
}

std:

#include<bits/stdc++.h>
using namespace std;
const int MAXN = 1000005;
const long long mod = (long long)1e9 + 7;
long long d[MAXN], ans;
int n;
void diff(long long a[])
{
    for (int i = n; i ; --i)
    {
        a[i] = (a[i] - a[i - 1]) % mod;
    }
    return;
}
int main()
{
    scanf("%d", &n);
    for (int i = 1; i <= n; ++i)
    {
        scanf("%lld", &d[i]);
    }
    diff(d);
    for (int i = 1; i <= n; ++i)
    {
        ans += max(d[i], 0LL);
    }
    printf("%lld\n", ans);
    return 0;
}