莫队算法
没有用线段树，而是看了showson的并查集%%%
1 #include<algorithm> 2 #include<iostream> 3 #include<cstdlib> 4 #include<cstring> 5 #include<cstdio> 6 #include<string> 7 #include<cmath> 8 #include<ctime> 9 #include<queue> 10 #include<stack> 11 #include<map> 12 #include<set> 13 #define rre(i,r,l) for(int i=(r);i>=(l);i--) 14 #define re(i,l,r) for(int i=(l);i<=(r);i++) 15 #define Clear(a,b) memset(a,b,sizeof(a)) 16 #define inout(x) printf("%d",(x)) 17 #define douin(x) scanf("%lf",&x) 18 #define strin(x) scanf("%s",(x)) 19 #define LLin(x) scanf("%lld",&x) 20 #define op operator 21 #define CSC main 22 typedef unsigned long long ULL; 23 typedef const int cint; 24 typedef long long LL; 25 using namespace std; 26 void inin(int &ret) 27 { 28 ret=0;int f=0;char ch=getchar(); 29 while(ch<'0'||ch>'9'){if(ch=='-')f=1;ch=getchar();} 30 while(ch>='0'&&ch<='9')ret*=10,ret+=ch-'0',ch=getchar(); 31 ret=f?-ret:ret; 32 } 33 int n,m,a[50050],wei[50050],temp; 34 int fa[50050],s[50050],bo[50050],pos[50050],sta[50050],top,ANS[50050]; 35 struct que 36 { 37 int l,r,id; 38 void in(int i){inin(l),inin(r),id=i;} 39 bool op < (const que &rhs)const {return wei[l]==wei[rhs.l]?r<rhs.r:l<rhs.l;} 40 }q[50050]; 41 int find(int x){return x==fa[x]?x:fa[x]=find(fa[x]);} 42 void merge(int x,int y) 43 { 44 x=find(x),y=find(y); 45 if(x==y)return ; 46 s[x]+=s[y]; 47 temp=max(temp,s[x]); 48 fa[y]=x; 49 } 50 void init() 51 { 52 re(i,1,n)fa[i]=i,s[i]=0; 53 temp=1; 54 } 55 void add(int x) 56 { 57 bo[x]=1; 58 s[x]=1; 59 if(bo[x-1])merge(x-1,x); 60 if(bo[x+1])merge(x,x+1); 61 } 62 int main() 63 { 64 inin(n);inin(m); 65 int nn=sqrt(n); 66 re(i,1,n)inin(a[i]),wei[i]=(i-1)/nn+1,pos[a[i]]=i; 67 re(i,1,m)q[i].in(i); 68 sort(q+1,q+m+1); 69 int r=0; 70 re(i,1,m) 71 { 72 if(i==1||wei[q[i].l]!=wei[q[i-1].l]) 73 { 74 Clear(bo,0);Clear(s,0); 75 init(),top=0; 76 int head=(q[i].l-1)/nn*nn+1; 77 r=min(head+nn-1,n); 78 re(j,head,r)sta[++top]=a[j]; 79 sort(sta+1,sta+top+1); 80 } 81 while(r<q[i].r)add(a[++r]); 82 int ans=temp,nl=1,nr=0; 83 re(j,1,top) 84 { 85 int c=sta[j]; 86 if(pos[c]<q[i].l||pos[c]>q[i].r)continue; 87 if(c==nr+1)nr+=s[find(c+1)]+1; 88 else 89 { 90 ans=max(ans,nr-nl+1); 91 nl=c-s[find(c-1)]; 92 nr=c+s[find(c+1)]; 93 } 94 } 95 ANS[q[i].id]=max(ans,nr-nl+1); 96 } 97 re(i,1,m)printf("%d ",ANS[i]); 98 return 0; 99 }