hdu 2665 Kth number（主席树）

Kth number

Problem Description
Give you a sequence and ask you the kth big number of a inteval.

Input
The first line is the number of the test cases.
For each test case, the first line contain two integer n and m (n, m <= 100000), indicates the number of integers in the sequence and the number of the quaere.
The second line contains n integers, describe the sequence.
Each of following m lines contains three integers s, t, k.
[s, t] indicates the interval and k indicates the kth big number in interval [s, t]

Output
For each test case, output m lines. Each line contains the kth big number.

Sample Input
1
10 1
1 4 2 3 5 6 7 8 9 0
1 3 2

Sample Output
2

ps：主席树模板题

代码：

#include<stdio.h>#include<string.h>#include<algorithm>using namespace std;const int maxn=100000+10;int rt[maxn*20],ls[maxn*20],rs[maxn*20],sum[maxn*20],a[maxn],b[maxn];int tot;void Build(int &o,int le,int ri){    o=++tot;    sum[o]=0;    if(le==ri)        return ;    int mid=(le+ri)>>1;    Build(ls[o],le,mid);    Build(rs[o],mid+1,ri);}void Update(int &o,int le,int ri,int last,int val){    o=++tot;    ls[o]=ls[last];    rs[o]=rs[last];    sum[o]=sum[last]+1;    if(le==ri)        return ;    int mid=(le+ri)>>1;    if(val<=mid)        Update(ls[o],le,mid,ls[last],val);    else        Update(rs[o],mid+1,ri,rs[last],val);}int Query(int st,int ed,int le,int ri,int val){    if(le==ri)        return le;    int mid=(le+ri)>>1;    int cnt=sum[ls[ed]]-sum[ls[st]];    if(val<=cnt)        return Query(ls[st],ls[ed],le,mid,val);    else        return Query(rs[st],rs[ed],mid+1,ri,val-cnt);}int main(){    int t,n,m;    scanf("%d",&t);    while(t--)    {        tot=0;        scanf("%d%d",&n,&m);        for(int i=1; i<=n; ++i)            scanf("%d",&a[i]),b[i]=a[i];        sort(b+1,b+1+n);        int ps=unique(b+1,b+1+n)-b-1;        for(int i=1; i<=n; ++i)            a[i]=lower_bound(b+1,b+1+ps,a[i])-b;        Build(rt[0],1,ps);        for(int i=1; i<=n; ++i)            Update(rt[i],1,ps,rt[i-1],a[i]);        while(m--)        {            int le,ri,val;            scanf("%d%d%d",&le,&ri,&val);            int ans=Query(rt[le-1],rt[ri],1,ps,val);            printf("%d\n",b[ans]);        }    }    return 0;}

主席树入门参考博客：
殇雪