HDU 2665 Kth number 主席树

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

题意：不修改查询区间第K个数

思路：主席树入门题。

/** @Date    : 2016-12-16-19.37
  * @Author  : Lweleth (SoungEarlf@gmail.com)
  * @Link    : https://github.com/
  * @Version :
  */
#include <bits/stdc++.h> 
#define LL long long
#define PII pair
#define MP(x, y) make_pair((x),(y))
#define fi first
#define se second
#define PB(x) push_back((x))
#define MMG(x) memset((x), -1,sizeof(x))
#define MMF(x) memset((x),0,sizeof(x))
#define MMI(x) memset((x), INF, sizeof(x))
using namespace std;

const int INF = 0x3f3f3f3f;
const int N = 1e5+10;
const double eps = 1e-8;

struct yuu
{
    int ls, rs;
    int sum;
}tt[N * 20];//

int tot = 0;
int a[N], b[N];
int rt[N * 20];
int n, m, k, x, y, T, sq;

void build(int l, int r, int &p)
{
    p = ++tot;

    tt[p].sum = 0;
    if(l == r)
        return ;
    int mid = (l + r) >> 1;
    build(l, mid, tt[p].ls);
    build(mid + 1, r, tt[p].rs);
}

void updata(int l, int r, int pre, int &p, int v)
{
    p = ++tot;
    tt[p].ls = tt[pre].ls;
    tt[p].rs = tt[pre].rs;
    tt[p].sum = tt[pre].sum + 1;

    if(l == r)
        return ;
    int mid = (l + r) >> 1;
    if(v <= mid)
        updata(l, mid, tt[pre].ls, tt[p].ls, v);
    else
        updata(mid + 1, r, tt[pre].rs, tt[p].rs, v);
}

int query(int l, int r, int pre, int nw, int s)
{
    if(l == r)
        return b[l];
    int mid = (l + r) >> 1;
    int q = tt[tt[nw].ls].sum - tt[tt[pre].ls].sum;
    if(s <= q)
        query(l, mid, tt[pre].ls, tt[nw].ls, s);
    else query(mid + 1, r, tt[pre].rs, tt[nw].rs, s - q);

}

int main()
{
    scanf("%d", &T);
    while(T--)
    {
        scanf("%d%d", &n, &m);
        for(int i = 1; i <= n; i++)
            scanf("%d", a + i), b[i] = a[i];
        sort(b + 1, b + 1 + n);
        sq = unique(b + 1, b + n + 1) - (b + 1);
        tot = 0;
        build(1, sq, rt[0]);
        for(int i = 1; i <= n; i++)
        {
            int v = lower_bound(b + 1, b + 1 + sq, a[i]) - b;
            a[i] = v;
        }
        for(int i = 1; i <= n; i++)
            updata(1, sq, rt[i - 1], rt[i], a[i]);
        while(m--)
        {
            scanf("%d%d%d", &x, &y, &k);
            int ans = query(1, sq, rt[x - 1], rt[y], k);
            printf("%d
", ans);
        }
    }
    return 0;
}