poj 3368

线段树

区间存储最大的频率

不习惯写RMQ还是线段树好了...

#include<cstdio>
#include<cstring>
#include<cmath>
#include<algorithm>
using namespace std;
int n,q;
struct node{
    int l,r;
    int amax,lmax,rmax;
}tree[300100];
int a[100100];
void build(int s,int t,int id){
    tree[id].l=s;
    tree[id].r=t;
    if(s==t){
        tree[id].amax=tree[id].lmax=tree[id].rmax=1;
        return ;
    }
    int mid=(s+t)>>1;
    build(s,mid,id*2);
    build(mid+1,t,id*2+1);

    //更新tree[id].amax
    int tem;
    if(a[tree[id*2].r]==a[tree[id*2+1].l])
        tem=tree[id*2].rmax+tree[id*2+1].lmax;
    else
        tem=0;
    tree[id].amax=max(max(tree[id*2].amax,tree[id*2+1].amax),tem);
    //更新tree[id].lmax
    tree[id].lmax=tree[id*2].lmax;
    if(tree[id*2].lmax==mid-s+1 && a[tree[id*2].r]==a[tree[id*2+1].l])            //这里要注意
        tree[id].lmax+=tree[id*2+1].lmax;

    //更新tree[id].rmax
    tree[id].rmax=tree[id*2+1].rmax;
    if(tree[id*2+1].rmax==t-mid && a[tree[id*2].r]==a[tree[id*2+1].l])            //这里要注意
        tree[id].rmax+=tree[id*2].rmax;
}
int query(int s,int t,int id){
    if(tree[id].l==s && tree[id].r==t)
        return tree[id].amax;
    int mid=(tree[id].l+tree[id].r)>>1;
    if(s>mid)
        return query(s,t,id*2+1);
    else if(t<=mid)
        return query(s,t,id*2);
    else{
        int a1=query(s,mid,id*2);
        int a2=query(mid+1,t,id*2+1);
        int a3=0;
        if(a[tree[id*2].r]==a[tree[id*2+1].l])
            a3=min(tree[id*2].rmax,mid-s+1)+min(tree[id*2+1].lmax,t-mid);          //这里要注意
        return max(max(a1,a2),a3);
    }
}
int main(){
    int i,j,u,v;
    while(scanf("%d",&n)){
        if(n==0)break;
        scanf("%d",&q);
        for(i=1;i<=n;i++)
            scanf("%d",&a[i]);
        build(1,n,1);
        for(i=1;i<=q;i++){
            scanf("%d %d",&u,&v);
            printf("%d\n",query(u,v,1));
        }
    }
}