hdu 1394——Minimum Inversion Number

線段樹

//31MS 340K c++#include<iostream>#include<cstdio>using namespace std;#define maxn 5010#define ls (rt<<1)#define rs (rt<<1|1)#define mid ((t[rt].l+t[rt].r)>>1)struct tree{int l,r;int sum;}t[maxn<<4];int num[maxn];void pushup(int rt){t[rt].sum=t[ls].sum+t[rs].sum;}void build(int rt,int l,int r){t[rt].l=l,t[rt].r=r,t[rt].sum=0;if(l==r)return ;build(ls,l,mid);build(rs,mid+1,r);}void add(int rt,int x){if(t[rt].l==t[rt].r){t[rt].sum=1;return ;}if(x<=mid)add(ls,x);elseadd(rs,x);pushup(rt);}int query(int rt,int l,int r){if(t[rt].l==l&&t[rt].r==r)return t[rt].sum;if(r<=mid)return query(ls,l,r);elseif(l>mid)return query(rs,l,r);elsereturn query(ls,l,mid)+query(rs,mid+1,r);}int main(){int n;while(~scanf("%d",&n)){build(1,0,n-1);int sum=0;for(int i=0;i<n;i++){scanf("%d",&num[i]);sum+=query(1,num[i],n-1);add(1,num[i]);}int ans=sum;for(int i=0;i<n-1;i++){sum+=n-1-2*num[i];ans=min(ans,sum);}printf("%d\n",ans);}return 0;}

 

樹狀數組

//15MS 308K  c++#include<cstdio>#include<iostream>using namespace std;#define maxn 5010int num[maxn];int t[maxn];int n;int lowbit(int x){return (-x)&x;}int Sum(int x){int sum=0;while(x>=1){sum+=t[x];x-=lowbit(x);}return sum;}void Update(int x){while(x<=n){t[x]++;x+=lowbit(x);}}int main(){while(~scanf("%d",&n)){memset(t,0,sizeof(t));int sum=0;for(int i=0;i<n;i++){scanf("%d",&num[i]);sum+=Sum(n)-Sum(num[i]+1);Update(num[i]+1);}int ans=sum;for(int i=0;i<n-1;i++){sum+=n-1-2*num[i];ans=min(sum,ans);}printf("%d\n",ans);}return 0;}