CODEVS 1743（伸展树区间翻转）

来源：互联网发布：linux 启动文件丢失编辑：程序博客网时间：2024/06/04 19:58

题目链接：http://codevs.cn/problem/1743/

#include <cstdio>#include <cstring>#include <algorithm>using namespace std;#define N 300010int c[N][2],fa[N],rev[N],v[N],sz[N];int n,rt;void pushup(int x){    int l=c[x][0],r=c[x][1];    sz[x]=sz[l]+sz[r]+1;}void build(int l,int r,int f){    if(l>r) return;    int now=l,last=f;    if(l==r)    {        sz[now]=1;fa[now]=last;        if(l<f) c[last][0]=now;        else c[last][1]=now;        return;    }    int mid=l+r>>1;now=mid;    build(l,mid-1,mid);build(mid+1,r,mid);    fa[now]=last;pushup(now);    if(l<f) c[last][0]=now;    else c[last][1]=now;}void rotate(int x,int &k){    int y=fa[x],z=fa[y],l,r;    if(c[y][0]==x) l=0;else l=1;r=l^1;    if(y==k) k=x;    else if(c[z][0]==y) c[z][0]=x;else c[z][1]=x;    fa[x]=z;fa[y]=x;fa[c[x][r]]=y;    c[y][l]=c[x][r];c[x][r]=y;    pushup(y);pushup(x);}void splay(int x,int &k){    int y,z;    while(x!=k)    {        //printf("%d %d ??\n",x,k);        y=fa[x];z=fa[y];        if(y!=k)        {            if(c[z][0]==y^c[y][0]==x) rotate(x,k);            else rotate(y,k);        }        else rotate(x,k);    }}void pushdown(int k){    int l=c[k][0],r=c[k][1];    if(rev[k])    {        rev[l]^=1;rev[r]^=1;        swap(c[k][0],c[k][1]);        rev[k]=0;    }}int find(int k,int rank){    pushdown(k);    int l=c[k][0],r=c[k][1];    if(rank<=sz[l]) return find(l,rank);    else if(rank==sz[l]+1) return k;    else return find(r,rank-sz[l]-1);}void reverse(int s,int t){    int x=find(rt,s-1),y=find(rt,t+1),z;    splay(x,rt);splay(y,c[x][1]);    z=c[y][0];rev[z]^=1;}int main(){    scanf("%d",&n);    for(int i=2;i<=n+1;++i)        scanf("%d",&v[i]);    build(1,n+2,0);rt=n+3>>1;    int ans=0,x,y,z;    while(true)    {        x=find(rt,2);        if(v[x]==1) break;        reverse(2,v[x]+1);        ++ans;    }    printf("%d\n",ans);    return 0;}

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