划分树模板

POJ2104

//划分树，查询区间第k大

原理以后补上。

#include <set>
#include <map>
#include <list>
#include <cmath>
#include <ctime>
#include <deque>
#include <queue>
#include <stack>
#include <cctype>
#include <cstdio>
#include <string>
#include <vector>
#include <cassert>
#include <cstdlib>
#include <cstring>
#include <sstream>
#include <iostream>
#include <algorithm>
using namespace std;
//划分树，查询区间第k大
const int MAXN = 100010;
int tree[20][MAXN]; // 表示每层每个位置的值
int sorted[MAXN]; // 已经排好序的数
int toleft[20][MAXN] ;// toleft[p][i] 表示第i层从1到i有数分入左边

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);
}
//查询区间第K大的数，[L,R]是大区间，[l,r]是要查询的小区间
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) == 2){
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+n+1);
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;
}