HDOJ 1032

司马杭电！大家注意测试数据，第一个不一定比第二个小。害得我调了一小时。

The 3n + 1 problem

#include <iostream>
#include <cstdio>

typedef long long ll;

using namespace std;

const int N = 1000001;

int len[N];

int length(int n){
    if(len[n])return len[n];
    int count = 1;
    int pn = n;
    while(n!=1){
        if(n%2==1)n = 3*n+1;
        else n = n/2;
        if(n<N&&len[n]){
            count+=len[n];
            break;
        }
        count++;
    }
    return len[pn] = count;
}

void swap(int& a,int& b){
    int temp = a;
    a = b;
    b = temp;
}

int main(){
    int a,b;
    ll max;
    while(cin>>a>>b){
        cout<<a<<" "<<b<<" ";
        if(a>b)swap(a,b);
        max = length(a);
        for(int i = a+1;i<=b;++i){
            if(length(i)>max)max = length(i);
        }
        cout<<max<<endl;
    }
    return 0;
}