SPOJ - 3267. D-query 主席树求区间个数

SPOJ - 3267

主席树的又一种写法。 从后端点开始添加主席树， 然后如果遇到出现过的元素先把那个点删除， 再更新树， 最后查询区间就好了。

 #include<bits/stdc++.h>
 using namespace std;
 #define Fopen freopen("_in.txt","r",stdin); freopen("_out.txt","w",stdout);
 #define LL long long
 #define ULL unsigned LL
 #define fi first
 #define se second
 #define pb push_back
 //#define lson l,m,rt<<1
 //#define rson m+1,r,rt<<1|1
 #define max3(a,b,c) max(a,max(b,c))
 #define min3(a,b,c) min(a,min(b,c))
 typedef pair<int,int> pll;
 const int INF = 0x3f3f3f3f;
 const LL mod =  (int)1e9+;
 const int N = 3e4 + ;
 const int M = 1e6 + ;
 int root[N], lson[M], rson[M], cnt[M];
 int a[N];
 map<int,int> mp;
 int tot;
 int Build(int l, int r){
     int now = ++tot;
     cnt[now] = ;
     if(l < r){
         int m = l+r >> ;
         lson[now] = Build(l, m);
         rson[now] = Build(m+, r);
     }
     return now;
 }
 int Update(int l, int r, int pre, int c, int v){
     int now = ++tot;
     cnt[now] = cnt[pre] + v;
     if(l < r){
         int m = l+r >> ;
         if(c <= m){
             rson[now] = rson[pre];
             lson[now] = Update(l, m, lson[pre], c, v);
         }
         else {
             lson[now] = lson[pre];
             rson[now] = Update(m+, r, rson[pre], c, v);
         }
     }
     return now;
 }
 int Query(int l, int r, int p, int R){
     if(l == r) return cnt[p];
     int m = l+r >> ;
     if(R <= m){
         return Query(l, m, lson[p], R);
     }
     else {
         return Query(m+,r,rson[p],R) + cnt[lson[p]];
     }
 }
 int main(){
     int n;
     scanf("%d", &n);
     for(int i = ; i <= n; i++) scanf("%d", &a[i]);
     root[n+] = Build(, n);
     for(int i = n; i >= ; i--){
         if(mp[a[i]] == ){
             root[i] = Update(, n, root[i+], i, );
         }
         else {
             int tmp = Update(, n, root[i+], mp[a[i]], -);
             root[i] = Update(, n, tmp, i, );
         }
         mp[a[i]] = i;
     }
     int m, l, r;
     scanf("%d", &m);
     for(int i = ; i <= m; i++){
         scanf("%d%d", &l, &r);
         printf("%d\n", Query(,n,root[l],r));
     }
     return ;

 }

SPOJ-3267