POJ3666-Making the Grade（左偏树 or DP）

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;

const int N = 2005;
typedef long long ll;

struct LTree {
    int l, r, sz;
    int key, dis;
    bool operator<(const LTree lt) const {
        return key < lt.key;
    }
} tr[N];
int cnt_tr;

int NewTree(int k) {
    tr[++cnt_tr].key = k;
    tr[cnt_tr].l = tr[cnt_tr].r = tr[cnt_tr].dis = 0;
    tr[cnt_tr].sz = 1;
    return cnt_tr;
}

int Merge(int x, int y) {
    if (!x || !y) return x + y;
    if (tr[x] < tr[y]) swap(x, y);
    tr[x].r = Merge(tr[x].r, y);
    if (tr[tr[x].l].dis < tr[tr[x].r].dis) swap(tr[x].l, tr[x].r);
    tr[x].dis = tr[tr[x].r].dis + 1;
    tr[x].sz = tr[tr[x].l].sz + tr[tr[x].r].sz + 1;
    return x;
}

int Top(int x) {
    return tr[x].key;
}

void Pop(int &x) {
    x = Merge(tr[x].l, tr[x].r);
}

int a[N], root[N], num[N];

int main() {
    int n;
    while (~scanf("%d",&n)) {
        ll sum, tmp, ans;
        cnt_tr = sum = tmp = 0;
        for (int i = 0; i < n; ++i) {
            scanf("%d", a+i);
            sum += a[i];
        }
        int cnt = 0;
        for (int i = 0; i < n; ++i) {
            root[++cnt] = NewTree(a[i]);
            num[cnt] = 1;
            while (cnt > 1 && Top(root[cnt]) < Top(root[cnt-1])) {
                cnt--;
                root[cnt] = Merge(root[cnt], root[cnt+1]);
                num[cnt] += num[cnt+1];
                while (tr[root[cnt]].sz*2 > num[cnt]+1) Pop(root[cnt]);
            }
        }
        int px = 0;
        for (int i = 1; i <= cnt; ++i)
            for (int j = 0, x = Top(root[i]); j < num[i]; ++j)
                tmp += abs(a[px++]-x);
        ans = tmp;

        printf("%lld\n", ans);
    }
    return 0;
}