莫队 p4137

 1 #include<cstdio>
 2 #include<algorithm>
 3 #include<math.h>
 4 #include<string.h>
 5 using namespace std;
 6 const int maxn=2e5+10;
 7 int num[maxn];
 8 int answer,block;
 9 int vis[maxn];
10 struct node
11 {
12     int l,r,id;
13     int Ans;
14 }ans[maxn];
15 bool cmp(node x,node y)
16 {
17     if(x.l/block!=y.l/block)
18         return x.l<y.l;
19     if(x.l/block&1)        //使用波形排序，可进一步的优化
20         return x.r<y.r;
21     return x.r>y.r;
22 }
23 bool CMP(node x,node y)
24 {
25     return x.id<y.id;
26 }
27 void Delete(int pos)
28 {
29     vis[num[pos]]--;
30     if(!vis[num[pos]]&&num[pos]<answer){
31         answer=num[pos];
32     }
33 }
34 void add(int pos)
35 {
36     vis[num[pos]]++;
37     if(vis[num[pos]]==1&&answer==num[pos]){
38         int tmp=answer+1;
39         while(1){
40             if(!vis[tmp]){
41                 answer=tmp;
42                 return;
43             }
44             tmp++;
45         }
46     }
47 }
48 int main()
49 {
50     int n,m;
51     scanf("%d%d",&n,&m);
52     block=sqrt(n);
53     for(int i=1;i<=n;i++) scanf("%d",&num[i]);
54     for(int i=1;i<=m;i++){
55         scanf("%d%d",&ans[i].l,&ans[i].r);
56         ans[i].id=i;
57     }
58     sort(ans+1,ans+1+m,cmp);
59     int left=1,right=0;
60     for(int i=1;i<=m;i++){
61         while(ans[i].l>left) Delete(left++);
62         while(ans[i].l<left) add(--left);
63         while(ans[i].r>right) add(++right);
64         while(ans[i].r<right) Delete(right--);
65         ans[i].Ans=answer;
66     }
67     sort(ans+1,ans+1+m,CMP);
68     for(int i=1;i<=m;i++)
69         printf("%d\n",ans[i].Ans);
70     return 0;
71 }