HDU 2665 Kth number 划分树

题目：http://acm.hdu.edu.cn/showproblem.php?pid=2665

题意：求给定区间中的第k大值

思路：划分树模板题

#include 
#include 
#include 
#include 
using namespace std;

const int N = 100010;
struct node
{
    int l, r;
}s[N*4];
int n, m;
int arr[N], arrs[N], cut[20][N], seg[20][N];
void build(int d, int l, int r, int k)
{
    s[k].l = l, s[k].r = r;
    if(l == r) return;
    int mid = (l + r) >> 1, lb = l, rb = mid + 1, cnt = mid - l + 1;
    for(int i = l; i <= mid; i++)
        if(arrs[i] < arrs[mid])
            cnt--;
    for(int i = l; i <= r; i++)
    {
        if(i == l) cut[d][i] = 0;
        else cut[d][i] = cut[d][i-1];
        if(seg[d][i] == arrs[mid])
        {
            if(cnt)
                cnt--, cut[d][i]++, seg[d+1][lb++] = seg[d][i];
            else seg[d+1][rb++] = seg[d][i];
        }
        else if(seg[d][i] < arrs[mid])
            cut[d][i]++, seg[d+1][lb++] = seg[d][i];
        else seg[d+1][rb++] = seg[d][i];
    }
    build(d + 1, l, mid, k << 1);
    build(d + 1, mid + 1, r, k << 1|1);
}
int query(int d, int l, int r, int x, int k)
{
    if(s[k].l == s[k].r)
        return seg[d][s[k].l];
    int mid = (s[k].l + s[k].r) >> 1, ls, lss;
    if(s[k].l == l) ls = 0, lss = cut[d][r];
    else ls = cut[d][l-1], lss = cut[d][r] - ls;
    if(x <= lss) return query(d + 1, s[k].l + ls, s[k].l + ls + lss - 1, x, k << 1);
    else return query(d + 1, mid + 1 + l - s[k].l - ls, mid + 1 + r - s[k].l - ls - lss, x - lss, k << 1|1);
}
int main()
{
    int t, a, b, c;
    scanf("%d", &t);
    while(t--)
    {
        scanf("%d%d", &n, &m);
        for(int i = 1; i <= n; i++)
        {
            scanf("%d", arr + i);
            seg[0][i] = arrs[i] = arr[i];
        }
        sort(arrs + 1, arrs + 1 + n);
        build(0, 1, n, 1);

        while(m--)
        {
            scanf("%d%d%d", &a, &b, &c);
            printf("%d\n", query(0, a, b, c, 1));
        }
    }
    return 0;
}