hdu 4251 划分树入门题

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <algorithm>
#include <cstring>
#include <cmath>
#include <stack>
#include <vector>
#include <queue>
#include <map>
#include <set>
#include <climits>
#include <cassert>
#define LL long long
#define lson lo, mi, rt << 1
#define rson mi + 1, hi, rt << 1 | 1

using namespace std;
const int maxn = 1e5 + 10;
const int inf = 0x3f3f3f3f;
const double eps = 1e-8;
const double pi = acos(-1.0);
const double ee = exp(1.0);

int tree[30][maxn];     //表示每层每个位置的值
int sorted[maxn];       //排完序的数
int toleft[30][maxn];   //toleft[p][i]表示第p层从1到i有多少个数在左边

void build(int l, int r, int dep)
{
if (l == r)
return;
int mi = (l + r) >> 1;
int same = mi - l + 1;          //等于中位数的数字个数
for (int i = l; i <= r; i++)
{
if (tree[dep][i] < sorted[mi])
{
same--;
}
}

int lpos = l;
int rpos = mi + 1;
for (int i = l; i <= r; i++)
{
if (tree[dep][i] < sorted[mi])//比中位数小
{
tree[dep + 1][lpos++] = tree[dep][i];
}
else if (tree[dep][i] == sorted[mi] && same > 0)
{
tree[dep + 1][lpos++] = tree[dep][i];
same--;
}
else                          //比中位数大
{
tree[dep + 1][rpos++] = tree[dep][i];
}
toleft[dep][i] = toleft[dep][l - 1] + lpos - l; // - l  不是减一
}
build(l, mi, dep + 1);
build(mi + 1, r, dep + 1);
}

//查询区间第k大数
int query(int L, int R, int l, int r, int dep, int k)
{
if (l == r)
return tree[dep][l];
int mi = (L + R) >> 1;
int cnt = toleft[dep][r] - toleft[dep][l - 1];
if (k <= cnt)
{
int nextl = L + toleft[dep][l - 1] - toleft[dep][L - 1];
int nextr = nextl + cnt - 1;
return query(L, mi, nextl, nextr, dep + 1, k);
}
else
{
int nextr = r + toleft[dep][R] - toleft[dep][r];
int nextl = nextr - (r - l - cnt);
return query(mi + 1, R, nextl, nextr, dep + 1, k - cnt);
}
}

int main()
{
#ifdef LOCAL
freopen("in.txt", "r", stdin);
#endif // LOCAL
int n, m;
int ca = 1;
while (~scanf("%d", &n))
{
memset(tree, 0, sizeof(tree));
memset(toleft, 0, sizeof(toleft));
for (int i = 1; i <= n; i++)//start from 1
{
scanf("%d", &tree[0][i]);
sorted[i] = tree[0][i];
}
sort(sorted + 1, sorted + n + 1);
build(1, n, 0);
scanf("%d", &m);
printf("Case %d:\n", ca++);
while (m--)
{
int fr, to;
scanf("%d%d", &fr, &to);
printf("%d\n", query(1, n, fr, to, 0, ((to - fr) >> 1) + 1));
}
}
return 0;
}