SPOJ D-QUERY

以前主席树学  kungbin 最近看了网上的版本 终于发现和我以前学的线段树差不多的了 希望最近能够加强

#include<bits/stdc++.h>
using namespace std;
const int INF = 0x3f3f3f3f;
const int MOD = 1e9+7;
const int MAXN = 30005;

struct Node{
	int ls,rs, sum;
}tree[MAXN*25];
int tot;
int a[MAXN];
int vis[1000006];
int root[MAXN];

int Build(int l,int r) {
	int rt = tot++;
	tree[rt].sum = 0;
	if(l == r) return rt;
	int m = (l+r) >>1;
	tree[rt].ls = Build(l,m);
	tree[rt].rs = Build(m+1,r);
	return rt;
}
int Update(int pos,int num,int pre,int l,int r) {
	int rt = tot++;
	tree[rt] = tree[pre];
   	tree[rt].sum += num;
	if(l == r) return rt;
	int m = (l+r) >>1;
	if(pos <= m) tree[rt].ls = Update(pos,num,tree[pre].ls,l,m);
	else tree[rt].rs = Update(pos,num,tree[pre].rs,m+1,r);
	return rt;
}
int Query(int rt,int L,int R,int l,int r) {
	if(L <= l && r <= R) {
		return tree[rt].sum;
	}
	int m = (l+r)>>1;
	int ans = 0;
	if(L <= m) ans += Query(tree[rt].ls, L,R,l,m);
	if(R > m) ans += Query(tree[rt].rs, L,R,m+1,r);
	return ans;
}
int main(){
	int n,m;
	while(~scanf("%d",&n)) {
		tot = 0;
		memset(vis,0,sizeof(vis));
		for(int i = 1; i <= n; ++i) {
			scanf("%d",&a[i]);
		}
		root[0] = Build(1,n);
		for(int i = 1; i <= n; ++i) {
			int tt = Update(i,1,root[i-1],1,n);
			if(vis[a[i]]) {
				root[i] = Update(vis[a[i]],-1,tt,1,n);
			}else root[i] = tt;
			vis[a[i]] = i;
		}
		scanf("%d",&m);
		for(int i = 1; i <= m; ++i) {
			int a,b; scanf("%d %d",&a,&b);
			printf("%d\n", Query(root[b],a,b,1,n));
		}
	}
	return 0;
}