hdu 4251 划分树（板子题）

题意：给定一个数组，求区间中位数，保证给定区间长度是奇数

思路：划分树求区间中位数

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
#define MAX_SIZE 100005  
int sorted[MAX_SIZE];//已经排好序的数据  
int toleft[25][MAX_SIZE];  
int tree[25][MAX_SIZE];  
void build_tree(int left, int right, int deep)   
{  
    int i;  
    if (left == right) return ;  
    int mid = (left + right) >> 1;  
    int same = mid - left + 1; //位于左子树的数据  
    for (i = left; i <= right; ++i) {//计算放于左子树中与中位数相等的数字个数  
        if (tree[deep][i] < sorted[mid]) {  
            --same;  
        }  
    }  
    int ls = left;  
    int rs = mid + 1;  
    for (i = left; i <= right; ++i) {  
        int flag = 0;  
        if ((tree[deep][i] < sorted[mid]) || (tree[deep][i] == sorted[mid] && same > 0)) {  
            flag = 1;  
            tree[deep + 1][ls++] = tree[deep][i];  
            if (tree[deep][i] == sorted[mid])  
                same--;  
        } else {  
            tree[deep + 1][rs++] = tree[deep][i];  
        }  
        toleft[deep][i] = toleft[deep][i - 1]+flag;  
    }  
    build_tree(left, mid, deep + 1);  
    build_tree(mid + 1, right, deep + 1);  
}  
int query(int left, int right, int k, int L, int R, int deep)  
{  
    if (left == right)  
        return tree[deep][left];  
    int mid = (L + R) >> 1;  
    int x = toleft[deep][left - 1] - toleft[deep][L - 1];//位于left左边的放于左子树中的数字个数  
    int y = toleft[deep][right] - toleft[deep][L - 1];//到right为止位于左子树的个数  
    int ry = right - L - y;//到right右边为止位于右子树的数字个数  
    int cnt = y - x;//[left,right]区间内放到左子树中的个数  
    int rx = left - L - x;//left左边放在右子树中的数字个数  
    if (cnt >= k) {  
        //printf("sss %d %d %d\n", xx++, x, y);  
        return query(L + x, L + y - 1, k, L, mid, deep + 1);
        // 因为x不在区间内 所以没关系 所以先除去，从L+x开始，然后确定范围
    }  
    else {  
        //printf("qqq %d %d %d\n", xx++, x, y);  
        return query(mid + rx + 1, mid + 1 + ry, k - cnt, mid + 1, R, deep + 1); 
        //同理 把不在区间内的 分到右子树的元素数目排除，确定范围 
    }  
}  
int main()  
{  
    int m, n;  
    int a, b, k;  
    int i,cas=1;  
    while (scanf("%d",&n) !=EOF ) {  
        for (i = 1; i <= n; ++i) {  
            scanf("%d", &sorted[i]);  
            tree[0][i] = sorted[i];  
        }  
        sort(sorted + 1, sorted + 1 + n);  
        build_tree(1, n, 0);  
        scanf("%d",&m);
        printf("Case %d:\n",cas++ );
        for (i = 0; i < m; ++i) {  
            scanf("%d%d", &a, &b);  
            printf("%d\n", query(a, b, (b-a)/2+1, 1, n, 0));  
        }  
    }  
    return 0;  
}