題目鏈接:https://www.luogu.org/problemnew/show/P3834
離散化後,套用主席樹模板
#include<bits/stdc++.h>
using namespace std;
const int maxn = (int) (2e5 + 5);
int a[maxn],n,rt[maxn]; //rt爲版本號
vector <int > vec;
struct pstree
{
struct pst
{
int lch,rch,val;
}z[maxn * 20];
int cnt; // 節點個數
inline void insert(int &p, int pre, int l, int r, int q) // 更新後插入
{
p = ++cnt; // 版本號
z[p] = z[pre]; // 將當前版本初始化與前一個版本相同
++z[p].val;
if (l == r)
return;
int mid=(l + r) >> 1;
if (q <= mid)
insert(z[p].lch, z[pre].lch, l, mid, q); //更新左兒子
else
insert(z[p].rch, z[pre].rch, mid + 1, r, q); // 更新右兒子
}
inline int query (int l1, int r1, int l, int r, int q) // 查找
{
if (l == r)
return l;
int mid = (l + r) >> 1;
int tmp = z[ z[r1].lch ].val - z[ z[l1].lch ].val;
if (tmp >= q)
return query(z[l1].lch, z[r1].lch, l, mid, q); // 在左兒子中找
else
return query(z[l1].rch, z[r1].rch, mid + 1, r, q - tmp); // 在右兒子中找
}
}pstree;
int main()
{
// freopen("in.txt", "r", stdin);
int m;
scanf("%d%d", &n, &m);
for(int i = 1; i <= n; ++i)
{
scanf("%d", &a[i]);
vec.push_back(a[i]);
}
sort(vec.begin(), vec.end());
vec.erase(unique(vec.begin(), vec.end()), vec.end());
for (int i = 1; i <= n; ++i)
{
a[i] = lower_bound(vec.begin(), vec.end(), a[i]) - vec.begin() + 1;
pstree.insert(rt[i], rt[i - 1], 1, n, a[i]);
}
while (m--)
{
int l,r,k;
scanf("%d%d%d", &l, &r, &k);
int tmp = pstree.query(rt[l - 1], rt[r], 1, n, k) - 1;
printf("%d\n", vec[tmp]);
}
return 0;
}