poj 3368_2

线段树

代码：

#include<iostream>
#include<fstream>

using namespace std;

int n,m;

struct e{
	int l,r,max,maxl,maxr;
};

e tree[300001];
int b[100001];

void build(int s,int t,int p){
	int i,j,k;
	tree[p].l=s;
	tree[p].r=t;
	if(s==t)
	{
		tree[p].max=tree[p].maxl=tree[p].maxr=1;
		return;
	}
	k=(s+t)>>1;
	build(s,k,p*2);
	build(k+1,t,p*2+1);
	
	tree[p].maxl=tree[2*p].maxl;
	if(tree[2*p].maxl==k-s+1&&b[k]==b[k+1])
		tree[p].maxl+=tree[2*p+1].maxl;
	
	tree[p].maxr=tree[2*p+1].maxr;
	if(tree[2*p+1].maxr==t-k&&b[k]==b[k+1])
		tree[p].maxr+=tree[2*p].maxr;
	
	i=0;
	if(b[k]==b[k+1])
		i=tree[2*p].maxr+tree[2*p+1].maxl;
	j=max(tree[2*p].max,tree[2*p+1].max);
	tree[p].max=max(i,j);
}

void  find(int s,int t ,int p,int &x,int &y,int &sum){
	if(s<=tree[p].l&&tree[p].r<=t)
	{
		x=tree[p].maxl;
		y=tree[p].maxr;
		sum=tree[p].max;
		return;
	}
	if(t<=tree[2*p].r) find(s,t,p*2,x,y,sum);
	else
		if(s>=tree[2*p+1].l) find(s,t,2*p+1,x,y,sum);
		else
		{
			int i,j,k,i1,j1,k1;
			find(s,t,2*p,i1,j1,k1);
			find(s,t,2*p+1,i,j,k);
			int mid=tree[2*p].r;
			x=i1;
			if(b[mid]==b[mid+1]&&i1==mid-max(s,tree[p].l)+1)
				x+=i;
			
			y=j;
			if(b[mid]==b[mid+1]&&j==min(t,tree[p].r)-mid)
				y+=j1;

			sum=0;
			sum=max(k1,k);
			if(b[mid]==b[mid+1])
				sum=max(sum,j1+i);
		}
}

void read(){
//	ifstream cin("in.txt");
	int i,j,k,s,t,x,y,sum;
	while(scanf("%d",&n)!=EOF)
	{
		
		if(n==0) return;
		scanf("%d",&m);
		//cin>>m;
		for(i=1;i<=n;i++)
			scanf("%d",&b[i]);
			//cin>>b[i];
		build(1,n,1);
		
		for(i=1;i<=m;i++)
		{
			//cin>>s>>t;
			scanf("%d%d",&s,&t);
			find(s,t,1,x,y,sum);
			cout<<sum<<endl;
		}
	}

}

int main(){
	read();
	return 0;
}