洛谷 P1972 [SDOI2009]HH的项链 (可持久化线段树)

代码

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <cstdlib>
#include <algorithm>
#define N 50005
#define NN 1000005

using namespace std;

int n, cur, m, last[NN], p
;

struct Tnode{
Tnode *lson, *rson;
int sum;
}tree[N*20], *Root
;

Tnode *NewTnode(){
tree[cur].lson = tree[cur].rson = tree;
tree[cur].sum = 0;
return tree+cur++;
}

void update(Tnode *root, int L, int R, int x, int val){
if(L == x && R == x){
root->sum += val;
return;
}
int mid = (L + R) >> 1;
Tnode *p = NewTnode();
if(x <= mid){
*p = *root->lson;
root->lson = p;
update(p, L, mid, x, val);
}
else{
*p = *root->rson;
root->rson = p;
update(p, mid+1, R, x, val);
}
root->sum = root->lson->sum + root->rson->sum;
}

int query(Tnode *root, int L, int R, int x, int y){
if(x > R || y < L)  return 0;
if(x <= L && y >= R)  return root->sum;
int mid = (L + R) >> 1;

int tmp1 = query(root->lson, L, mid, x, y);
int tmp2 = query(root->rson, mid+1, R, x, y);
return tmp1 + tmp2;
}

int main(){

scanf("%d", &n);

for(int i = 1; i <= n; i++)  scanf("%d", &p[i]);

memset(last, -1, sizeof(last));

Root[0] = NewTnode();
for(int i = 1; i <= n; i++){
Root[i] = NewTnode();
*Root[i] = *Root[i-1];
if(~ last[p[i]])  update(Root[i], 1, n, last[p[i]], -1);
last[p[i]] = i;
update(Root[i], 1, n, i, 1);
}

scanf("%d", &m);
int a, b;
for(int i = 1; i <= m; i++){
scanf("%d%d", &a, &b);
printf("%d\n", query(Root[b], 1, n, a, b));
}

return 0;
}