bzoj 1045: [HAOI2008] 糖果传递

#include <iostream>
#include <vector>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <map>
#include <set>
#include <string>
#include <queue>
#include <stack>
#include <bitset>
using namespace std;
#define pb(x) push_back(x)
#define ll long long
#define mk(x, y) make_pair(x, y)
#define lson l, m, rt<<1
#define mem(a) memset(a, 0, sizeof(a))
#define rson m+1, r, rt<<1|1
#define mem1(a) memset(a, -1, sizeof(a))
#define mem2(a) memset(a, 0x3f, sizeof(a))
#define rep(i, n, a) for(int i = a; i<n; i++)
#define fi first
#define se second
typedef pair<int, int> pll;
const double PI = acos(-1.0);
const double eps = 1e-8;
const int mod = 1e9+7;
const int inf = 1061109567;
const int dir[][2] = { {-1, 0}, {1, 0}, {0, -1}, {0, 1} };
int a[1000005], pre[1000005];
int main()
{
    ll n, sum = 0;
    cin>>n;
    for(int i = 1; i<=n; i++) {
        scanf("%d", &a[i]);
        sum+=a[i];
    }
    sum/=n;
    for(int i = 2; i<=n; i++) {
        pre[i] = pre[i-1]+a[i]-sum;
    }
    sort(pre+1, pre+1+n);
    ll ans = 0;
    int mid = pre[(n>>1)+1];
    for(int i = 1; i<=n; i++) {
        ans += abs(pre[i]-mid);
    }
    cout<<ans<<endl;
    return 0;
}