zerojudge d712 – the 3n + 1 problem

#define MAX 1000000
using namespace std;
int dp[MAX+1];
int seg[4000010];
int (long long n)
{
    if(n<=MAX && dp[n]!=-1) return dp[n];
    int a;
    if(n%2==0) a=solve(n/2)+1;
    else a=solve(3*n+1)+1;
    if(n<=MAX) dp[n]=a;
    return a;
}
void build(int l,int r,int idx)
{
    if(l==r) seg[idx]=dp[l];
    else
    {
        int mid=(l+r)/2;
        build(l,mid,idx*2);
        build(mid+1,r,idx*2+1);
        seg[idx]=max(seg[idx*2],seg[idx*2+1]);
    }
}
int query(int l,int r,int L,int R,int idx)
{
    if(l==L&&r==R) return seg[idx];
    int mid=(L+R)/2;
    if(r<=mid) return query(l,r,L,mid,idx*2);
    else if(l>mid) return query(l,r,mid+1,R,idx*2+1);
    else return max( query(l,mid,L,mid,idx*2), query(mid+1,r,mid+1,R,idx*2+1) );
}
int main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    
    memset(dp,-1,sizeof dp);
    dp[1]=1;
    for(int i=1;i<=MAX;i++)
        solve(i);
    build(1,MAX,1);
    
    int i,j,l,r;
    while(cin>>i>>j)
    {
        if(i>j) tie(l,r)=make_tuple(j,i);
        else tie(l,r)=make_tuple(i,j);
        cout<<i<<' '<<j<<' '<<query(l,r,1,MAX,1)<<endl;
    }
}