hdu 5172 GTY's gay friends（线段树最值）

int const N = 1000005;
int n,m;
int a[N];
ll sum[N];
int pre[N];
int F[N<<4];
int lastPos[N];



void PushUp(int rt){
    F[rt]=max( F[rt<<1],F[rt<<1|1] );
}
void build(int l,int r,int rt){
    if(l==r){
        F[rt]=pre[l];
        return;
    }
    int m=(l+r)>>1;
    build(lson);
    build(rson);
    PushUp(rt);
}
int query(int L,int R,int l,int r,int rt){
    if(L<=l && r<=R){
        return F[rt];
    }
    int m=(l+r)>>1;
    int ret=0;
    if(L<=m) ret=max( ret,query(L,R,lson) );
    if(R>m) ret=max( ret,query(L,R,rson) );
    return ret;
}



int main(){

    while(scanf("%d%d",&n,&m)!=EOF){
        sum[0]=0;
        rep(i,1,n){
            scanf("%d",&a[i]);
            sum[i]=sum[i-1]+a[i];
        }
        mem(lastPos,0);
        rep(i,1,n){
            pre[i]=lastPos[a[i]];
            lastPos[a[i]]=i;
        }
        build(1,n,1);

        while(m--){
            int L,R;
            scanf("%d%d",&L,&R);
            ll temp=(ll)1*(R-L+2)*(R-L+1)/2;
            if( ((sum[R]-sum[L-1])==temp)&&query(L,R,1,n,1)<L ){
                puts("YES");
            }
            else{
                puts("NO");
            }
        }
    }

    return 0;
}