劃分樹 POJ 2761 feed the dogs

題目連結：http://poj.org/problem?id=2761

代碼風格：notonlysuccess劃分樹http://www.notonlysuccess.com/index.php/divide-tree/

上面的網站對劃分樹有相當詳細的說明~~不再贅述

題目大意： 有n隻小狗，每個小狗有一個相對的魅力值，求第i隻小狗~第j隻小狗中魅力值第k大的那個小狗的魅力值是多少（即求區間[i, j]第k大的數）

直接附上代碼：

#include<cstdio>
#include<iostream>
#include<algorithm>
#include<cstring>
using namespace std;

#define lson l, m, rt << 1
#define rson m+1, r, rt << 1 | 1
#define mid int m = (l+r) >> 1

struct nod
{
	int l, r;
}p[1345678];

int val[20][200002];
int w[1898989];
int tol[20][200020];

void build(int l, int r, int rt, int ss)
{
	p[rt].l = l;
	p[rt].r = r;
	if(l == r)
		return ;
	mid ;
	int lsame = m - l + 1;
	int i;
	for(i = l; i <= r; i ++)
		if(val[ss][i] < w[m])
			lsame --;
	int lpos = l ;
	int rpos = m+1;
	int same = 1;
	for(i = l; i <= r; i ++)
	{
		if(l == i)
			tol[ss][i] = 0;
		else tol[ss][i] = tol[ss][i-1];
		if(val[ss][i] < w[m])
		{
			tol[ss][i] ++;
			val[ss+1][lpos ++] = val[ss][i];
		}
		else if(val[ss][i] > w[m])
		{
			val[ss+1][rpos ++] = val[ss][i];
		}
		else
		{
			if(same <= lsame)
			{
				tol[ss][i] ++;
				val[ss+1][lpos ++] = val[ss][i];
				same ++;
			}
			else {
				val[ss+1][rpos ++] = val[ss][i];
			}
		}
	}
	build(lson, ss+1);
	build(rson, ss+1);
}

int query(int k, int l, int r, int rt, int d)
{
	if(l == r)
		return val[d][l];
	int s, ss;
	if(l == p[rt].l )
	{
		s = tol[d][r];
		ss = 0;
	}
	else {
		s = tol[d][r] - tol[d][l-1];
		ss = tol[d][l-1];
	}
	if(k <= s)
	{
		int newl = ss + p[rt].l;
		int newr = ss + p[rt].l + s - 1;
		return query(k, newl, newr, rt << 1, d+1);
	}
	else
	{
		int b = r-l+1-s;
		int bb = l - p[rt].l - ss;
		int m = (p[rt].l + p[rt].r ) >> 1;
		int newl = bb + m + 1;
		int newr = bb + m + b;
		return query(k-s, newl, newr, rt << 1 | 1, d + 1);
	}
}

int main()
{
	int n, m;
	int a, b, c;
	while(scanf("%d%d", &n, &m) != EOF)
	{
		int i;
		for(i = 1; i <= n; i ++)
		{
			scanf("%d", &w[i]);
			val[0][i] = w[i];
		}
		sort(w+1, w+n+1);
		build(1, n, 1, 0);
		while(m --)
		{
			scanf("%d%d%d", &a, &b, &c);
			int k ;
			if(a <= b)
			k = query(c, a, b, 1, 0);
			else k = query(c, b, a, 1, 0);
			printf("%d\n", k);
		}
	}
	return 0;
}