主席树做法 感觉主席树是最好想到的做法呀 可能是我太菜了
#include<iostream>
#include<cstring>
#include<unordered_map>
using namespace std;
const int maxn = 1000010;
typedef struct node
{
int l, r;
int cnt;
}Node;
Node tr[maxn * 32];
int a[maxn];
int root[maxn], idx;
int n, m;
int build(int l, int r)
{
int p = ++ idx;
if(l == r) return p;
int mid = l + r >> 1;
tr[p].l = build(l, mid), tr[p].r = build(mid + 1, r);
return p;
}
int insert(int p, int l, int r, int x, int c)
{
int q = ++ idx;
tr[q] = tr[p];
if(l == r){
tr[q].cnt += c;
return q;
}
int mid = l + r >> 1;
if(x <= mid) tr[q].l = insert(tr[p].l, l, mid, x, c);
else tr[q].r = insert(tr[p].r, mid + 1, r, x, c);
tr[q].cnt = tr[tr[q].l].cnt + tr[tr[q].r].cnt;
return q;
}
int query(int l, int r, int Tl, int Tr, int p)
{
if(Tl >= l && Tr <= r) return tr[p].cnt;
int mid = Tl + Tr >> 1;
int res = 0;
if(l <= mid) res += query(l, r, Tl, mid, tr[p].l);
if(r > mid) res += query(l, r, mid + 1, Tr, tr[p].r);
return res;
}
int main()
{
unordered_map<int, int> mp;
scanf("%d", &n);
root[0] = build(1, n);
for(int i = 1; i <= n; i ++){
int x; scanf("%d", &x);
root[i] = insert(root[i - 1], 1, n, i, 1);
if(mp.count(x)) root[i] = insert(root[i], 1, n, mp[x], -1);
mp[x] = i;
}
scanf("%d", &m);
for(int i = 0; i < m; i ++){
int l, r; scanf("%d %d", &l, &r);
printf("%d\n", query(l, r, 1, n, root[r]));
}
return 0;
}
可以分块