poj 2104 K-th Number(划分树)

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初学划分树，http://blog.csdn.net/zxy_snow/article/details/6681086，在这里学的，模板套的kuangbin大牛的

#include <stdio.h>#include <string.h>#include <algorithm>using namespace std;const int MAXN = 100010;int tree[20][MAXN];int sorted[MAXN];int toleft[20][MAXN];void build(int l, int r, int dep){    if(l == r) return;    int mid = (l+r) >> 1;    int same = mid-l+1;    for(int i = l; i <= r; ++i)        if(tree[dep][i] < sorted[mid])            --same;    int lpos = l;    int rpos = mid+1;    for(int i = l; i <= r; ++i)    {        if(tree[dep][i] < sorted[mid])            tree[dep+1][lpos++] = tree[dep][i];        else if(tree[dep][i] == sorted[mid] && same > 0)        {            tree[dep+1][lpos++] = tree[dep][i];            --same;        }        else            tree[dep+1][rpos++] = tree[dep][i];        toleft[dep][i] = toleft[dep][l-1]+lpos-l;    }    build(l,mid,dep+1);    build(mid+1,r,dep+1);}int query(int L, int R, int l, int r, int dep, int k){    if(l == r) return tree[dep][l];    int mid = (L+R) >> 1;    int cnt = toleft[dep][r]-toleft[dep][l-1];    if(cnt >= k)    {        int newl = L + toleft[dep][l-1]-toleft[dep][L-1];        int newr = newl+cnt-1;        return query(L,mid,newl,newr,dep+1,k);    }    else    {        int newr = r + toleft[dep][R]-toleft[dep][r];        int newl = newr - (r-l-cnt);        return query(mid+1,R,newl,newr,dep+1,k-cnt);    }}int main(){    int n,m;    while(scanf("%d %d",&n,&m) != EOF)    {        memset(tree,0,sizeof(tree));        for(int i = 1; i <= n; ++i)        {            scanf("%d",&tree[0][i]);            sorted[i] = tree[0][i];        }        sort(sorted+1,sorted+1+n);        build(1,n,0);        int s,t,k;        while(m--)        {            scanf("%d %d %d",&s,&t,&k);            printf("%d\n",query(1,n,s,t,0,k));        }    }    return 0;}

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