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题意：
给一个数组n（1e5）个数，给一个范围（fr， to， k），求这个范围中第k大的数。
解析：
划分树入门。
bing神的模板。
坑爹的地方是把-l 看成了-1........
一直re。
代码：
poj 2104：
#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 | 1using 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 LOCALfreopen("in.txt", "r", stdin);#endif // LOCALint n, m;while (~scanf("%d%d", &n, &m)){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);while (m--){int fr, to, k;scanf("%d%d%d", &fr, &to, &k);printf("%d\n", query(1, n, fr, to, 0, k));}}return 0;
}
hdu 2665：
#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 | 1using 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 LOCALfreopen("in.txt", "r", stdin);#endif // LOCALint ncase;scanf("%d", &ncase);while (ncase--){int n, m;scanf("%d%d", &n, &m);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);while (m--){int fr, to, k;scanf("%d%d%d", &fr, &to, &k);printf("%d\n", query(1, n, fr, to, 0, k));}}return 0;
}
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