C++中更快地执行两个程序的可能解释(使用 Python 比较）?

>更新：C++程序(如下所示)在没有其他标志的情况下编译，即g++ program.cpp.然而，提高优化水平并不能改变蛮力比记忆技术运行得更快的事实(在我的机器上为 0.1 秒 VS 1 秒)。

上下文

我尝试计算具有最长 Collatz 序列的数字(<100 万)。我编写了一个蛮力算法，并将其与建议的优化程序(基本上使用记忆)进行了比较。

我的问题是：蛮力执行速度比C++中所谓的优化(记忆)版本更快的原因可能是什么？

在我在我的机器(Macbook Air)上的比较下方;时间在注释中的程序代码开头。

C++(蛮力)

/**
* runs in 1 second
*/
#include <iostream>
#include <vector>
unsigned long long nextSequence(unsigned long long n)
{
if (n % 2 == 0)
return n / 2;
else
{
return 3 * n + 1;
}
}
int main()
{
int max_counter = 0;
unsigned long long result;
for (size_t i = 1; i < 1000000; i++)
{
int counter = 1;
unsigned long long n = i;
while (n != 1)
{
n = nextSequence(n);
counter++;
}
if (counter > max_counter)
{
max_counter = counter;
result = i;
}
}
std::cout << result << " has " << max_counter << " sequences." << std::endl;
return 0;
}

C++(记忆)

/**
* runs in 2-3 seconds 
*/
#include <iostream>
#include <unordered_map>
int countSequence(uint64_t n, std::unordered_map<uint64_t, uint64_t> &cache)
{
if (cache.count(n) == 1)
return cache[n];
if (n % 2 == 0)
cache[n] = 1 + countSequence(n / 2, cache);
else
cache[n] = 2 + countSequence((3 * n + 1) / 2, cache);
return cache[n];
}
int main()
{
uint64_t max_counter = 0;
uint64_t result;
std::unordered_map<uint64_t, uint64_t> cache;
cache[1] = 1;
for (uint64_t i = 500000; i < 1000000; i++)
{
if (countSequence(i, cache) > max_counter)
{
max_counter = countSequence(i, cache);
result = i;
}
}
std::cout << result << std::endl;
return 0;
}

在Python中，记忆技术确实运行得更快。

蟒蛇(记忆)

# runs in 1.5 seconds
def countChain(n):
if n in values:
return values[n]
if n % 2 == 0:
values[n] = 1 + countChain(n / 2)
else:
values[n] = 2 + countChain((3 * n + 1) / 2)
return values[n]

values = {1: 1}
longest_chain = 0
answer = -1
for number in range(500000, 1000000):
if countChain(number) > longest_chain:
longest_chain = countChain(number)
answer = number
print(answer)

蟒蛇(蛮力)

# runs in 30 seconds

def countChain(n):
if n == 1:
return 1
if n % 2 == 0:
return 1 + countChain(n / 2)
return 2 + countChain((3 * n + 1) / 2)

longest_chain = 0
answer = -1
for number in range(1, 1000000):
temp = countChain(number)
if temp > longest_chain:
longest_chain = temp
answer = number
print(answer)