文章标题 POJ 2104: K-th Number（主席树）

题目 传送门

思路参考自http://www.cnblogs.com/zyf0163/p/4749042.html
代码：

////http://www.cnblogs.com/zyf0163/p/4749042.html//#include <iostream>#include <cstdio>#include <cstring>#include <string>#include <queue>#include <set>#include <map>#include <algorithm>#include <math.h>#include <vector>using namespace std;typedef long long ll;const int mod=1e9+7;const int maxn=1e5+10;int n,m; int a[maxn],b[maxn];int tot;int sum[maxn*20];int ls[maxn*20],rs[maxn*20],rt[maxn];void build(int &num,int l,int r){    num=++tot;    sum[num]=0;    if (l==r)return;    int mid=(l+r)/2;    build(ls[num],l,mid);    build(rs[num],mid+1,r);}void update(int &num,int l,int r,int last,int pos){    num=++tot;    ls[num]=ls[last];    rs[num]=rs[last];    sum[num]=sum[last]+1;    if (l==r)return;    int mid=(l+r)/2;    if (pos<=mid)update(ls[num],l,mid,ls[last],pos);    else update(rs[num],mid+1,r,rs[last],pos);}int query(int st,int ed,int l,int r,int k){    if (l==r)return l;    int mid=(l+r)/2;    int cnt=sum[ls[ed]]-sum[ls[st]];    if (cnt>=k)return query(ls[st],ls[ed],l,mid,k);    else return query(rs[st],rs[ed],mid+1,r,k-cnt);}int main(){    while (scanf ("%d%d",&n,&m)!=EOF){        for(int i=1;i<=n;i++){            scanf ("%d",&a[i]);            b[i]=a[i];        }        sort(b+1,b+1+n);        int sz=unique(b+1,b+1+n)-(b+1);        tot=0;        build(rt[0],1,sz);        for (int i=1;i<=n;i++){            a[i]=lower_bound(b+1,b+1+sz,a[i])-(b);            update(rt[i],1,sz,rt[i-1],a[i]);            //printf("rt =  %d,ls =  %d, rs = %d, sum = %d\n", rt[i], ls[i], rs[i], sum[rt[i]]);        }        int ql,qr,x;        while (m--){            scanf ("%d%d%d",&ql,&qr,&x);            int tmp=query(rt[ql-1],rt[qr],1,sz,x);            printf ("%d\n",b[tmp]);        }    }    return 0;}