Project Euler Problem 14-Longest Collatz sequence

记忆化搜索来一发。没想到中间会爆int

#include <bits/stdc++.h>
using namespace std;

const int MAXN = 1000000;
int dp[MAXN];

int dfs(long long num)
{
    if(num <= MAXN && dp[num]) return dp[num];
    if(num == 1) return (dp[num] = 1);

    if(num&1)
    {
        if(num <= MAXN) return (dp[num] = dfs(num*3+1)+1);
        else return dfs(num*3+1)+1;
    }
    else
    {
        if(num <= MAXN) return (dp[num] = dfs(num/2)+1);
        else return dfs(num/2)+1;
    }

}

int main()
{
    int len = 0,res,maxn = 0;
    for(int i = 1; i <= MAXN; ++i)
    {
        len = dfs(i);
        if(len > maxn)
        {
            maxn = len;
            res = i;
        }
    }
    printf("%d\n",res);
    return 0;
}