POJ2104 K-th Number （划分树模板）

POJ2104 K-th Number （题目链接）

求区间第k大

/*************************************************************************
File Name: A.cpp
ID: obsoles1
PROG:
LANG: C++
Mail: 384099319@qq.com
Created Time: 四 8/25 19:45:17 2016
************************************************************************/
#define MAX(x,y) ((x)>(y)?(x):(y))
#define MIN(x,y) ((x)<(y)?(x):(y))
#define EACH(it,v) for(__typeof((v).begin()) it=(v).begin();it!=(v).end();++it)
#define ABS(x,y) ((x)>(y)?((x)-(y)):((y)-(x)))
#define MEM0(x) memset(x,0,sizeof(x))
#define MEM1(x) memset(x,-1,sizeof(x))
#define MEMX(x) memset(x,0x3f,sizeof(x))
#define pb push_back
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<iostream>
using namespace std;
const int N=1e5+10,M=20;
struct node{
int num
,cnt
;
}tree[M];
int sorted
,ans;

void build(int t,int L,int R) {
if (L==R) return;
int mid=(L+R)>>1,key=sorted[mid],scnt=mid-L+1,i;
for (i=L; i<=R; ++i)
if (tree[t].num[i]<key) --scnt;
int l=L-1,r=mid,cnt=0;
for (i=L; i<=R; ++i) {
int num=tree[t].num[i];
if (num < key || (num == key && scnt)) {//把小于等于key的数放入左树，否则放入右树
if (num == key) --scnt;
++cnt;
tree[t+1].num[++l]=num;
} else tree[t+1].num[++r]=num;
tree[t].cnt[i]=cnt;//记录当前放入左树的数的个数
}
build(t+1,L,mid);
build(t+1,mid+1,R);
}

void query(int t,int L,int R,int l,int r,int k) {
if (L==R) {
ans=tree[t].num[L];
return;
}
int mid=(L+R)>>1,left=0,sum_l=tree[t].cnt[r],new_l,new_r;
if (L != l) {
left=tree[t].cnt[l-1];
sum_l-=left;
}
if (sum_l >= k) {
new_l=L+left;
new_r=new_l+sum_l-1;
query(t+1,L,mid,new_l,new_r,k);
} else {
new_l=mid+1+l-L-left;
new_r=new_l+r-l-sum_l;
query(t+1,mid+1,R,new_l,new_r,k-sum_l);
}
}

int main() {
int n,m,i,l,r,k;
while (~scanf("%d%d",&n,&m)) {
for (i=1; i<=n; ++i) {
scanf("%d",sorted+i);
tree[0].num[i]=sorted[i];
}
sort(sorted+1,sorted+n+1);
build(0,1,n);
while (m--) {
scanf("%d%d%d",&l,&r,&k);
query(0,1,n,l,r,k);
printf("%d\n",ans);
}
}
}