[HDU 6318] Swaps and Inversions

[题目链接]

http://acm.hdu.edu.cn/showproblem.php?pid=6318

[算法]

线段树 / 树状数组

[代码]

#include<bits/stdc++.h>
using namespace std;
#define MAXN 100010

long long i,n,x,y,len,ans,l,r,mid;
long long a[MAXN],rk[MAXN],tmp[MAXN];

struct SegmentTree
{
        struct Node
        {
                long long l,r;
                long long sum;
        } Tree[MAXN << ];
        inline void build(long long index,long long l,long long r)
        {
                long long mid;
                Tree[index].l = l;
                Tree[index].r = r;
                Tree[index].sum = ;
                if (l == r) return;
                mid = (l + r) >> ;
                build(index << ,l,mid);
                build(index <<  | ,mid + ,r);
        }
        inline void add(long long index,long long pos,long long val)
        {
                long long mid;
                Tree[index].sum += val;
                if (Tree[index].l == Tree[index].r) return;
                mid = (Tree[index].l + Tree[index].r) >> ;
                if (mid >= pos) add(index << ,pos,val);
                else add(index <<  | ,pos,val);
        }
        inline long long query(long long index,long long l,long long r)
        {
                long long mid;
                if (l > r) return ;
                if (Tree[index].l == l && Tree[index].r == r) return Tree[index].sum;
                mid = (Tree[index].l + Tree[index].r) >> ;
                if (mid >= r) return query(index << ,l,r);
                else if (mid +  <= l) return query(index <<  | ,l,r);
                else return query(index << ,l,mid) + query(index <<  | ,mid + ,r);
        }
} T;

int main()
{

        while (scanf("%lld%lld%lld",&n,&x,&y) != EOF)
        {
                for (i = ; i <= n; i++)
                {
                        scanf("%lld",&a[i]);
                        tmp[i] = a[i];
                }
                sort(tmp + ,tmp + n + ,greater<int>());
                len = ;
                for (i = ; i <= n; i++)
                {
                        if (tmp[i] != tmp[i - ])
                                tmp[++len] = tmp[i];
                }
                for (i = ; i <= n; i++)
                {
                        l = ; r = len;
                        while (l <= r)
                        {
                                mid = (l + r) >> ;
                                if (a[i] >= tmp[mid]) r = mid - ;
                                else l = mid + ;
                        }
                        rk[i] = l;
                }
                T.build(,,len);
                ans = ;
                for (i = ; i <= n; i++)
                {
                        ans += T.query(,,rk[i] - );
                        T.add(,rk[i],);
                }
                printf("%lld\n",1ll * ans * min(x,y));
        }
        return ;

}