hdu 5919 主席树入门题

Posted 2020-08-12 very_czy

主席树是从右往左初始化，每次把这个数出现过的位置消去，然后在当前位置加一。

然后我的做法是查两遍，第一遍能找出不同的个数，除一半；再用这个值查，一直到底，最后返回位置，比较套路的一题。

#include <stdio.h>
#include <string.h>
#include <iostream>
#include <algorithm>
#include <vector>
#include <queue>
#include <set>
#include <map>
#include <string>
#include <math.h>
#include <stdlib.h>
#include <time.h>
using namespace std;
map<int,int>mp;
const int MAXN = 200010;
const int M = MAXN * 50;
int n,q,tot;
int a[MAXN];
int rt[M],lson[M],rson[M],c[M];
int build(int l,int r)
{

    int root = tot++;
//    printf ("%d---%d,%d\n",l,r,root);
    c[root] = 0;
    if(l != r)
    {
        int mid = (l+r)>>1;
        lson[root] = build(l,mid);
        rson[root] = build(mid+1,r);
    }
    return root;
}
int update(int root,int pos,int val)
{
    int newroot = tot++;
    int tmp = newroot;
    c[newroot] = c[root] + val;
    int l = 1, r = n;
    while(l < r)
    {
        int mid = (l+r)>>1;
        if(pos <= mid)
        {
            lson[newroot] = tot++;
            rson[newroot] = rson[root];
            newroot = lson[newroot];
            root = lson[root];
            r = mid;
        }
        else
        {
            rson[newroot] = tot++;
            lson[newroot] = lson[root];
            newroot = rson[newroot];
            root = rson[root];
            l = mid+1;
        }
        c[newroot] = c[root] + val;
    }
    return tmp;
}
int query(int root,int pos)
{
    int ret = 0;
    int l = 1, r = n;
    while(pos < r)
    {
        int mid = (l+r)>>1;
        if(pos <= mid)
        {
            r = mid;
            root = lson[root];
        }
        else
        {
            ret += c[lson[root]];
            root = rson[root];
            l = mid+1;
        }
    }
    return ret + c[root];
}
int query_pos(int root,int val)
{
    int l = 1, r = n;
    while(l<r)
    {
        int mid = (l+r)>>1;
        if(val <= c[lson[root]])
        {
            r = mid;
            root = lson[root];
        }
        else
        {
            val-=c[lson[root]];
            root = rson[root];
            l = mid+1;
        }
    }
    return r;
}
int main()
{
    //freopen("in.txt","r",stdin);
    //freopen("out.txt","w",stdout);
    int T,ncas=1;
    scanf ("%d",&T);
    while(T--)
    {
        scanf ("%d%d",&n,&q);
        tot = 0;
        for(int i = 1; i <= n; i++)
            scanf("%d",&a[i]);
        rt[n+1] = build(1,n);

        mp.clear();
        for(int i = n; i>= 1; i--)
        {
            if(mp.find(a[i]) == mp.end())
            {
                rt[i] = update(rt[i+1],i,1);
            }
            else
            {
                int tmp = update(rt[i+1],mp[a[i]],-1);
                rt[i] = update(tmp,i,1);
            }
            mp[a[i]] = i;
        }

        int ans=0;
        printf ("Case #%d:",ncas++);
        while(q--)
        {
            int l,r;
            scanf("%d%d",&l,&r);
            l=(l+ans)%n+1;
            r=(r+ans)%n+1;
            if (l>r) swap(l,r);
            int dif=query(rt[l],r);
            ans=query_pos(rt[l],(dif+1)/2);
            printf(" %d",ans);
        }
        printf ("\n");
    }
    return 0;
}