ZOJ-2414

C++11处女题，时间竟然用了790ms，无语啊，咋会这么慢，感觉算法差不多啊。。算了下次用C++试下，妹的新特性的for循环和JAVA好像，用起来爽，不是是不是因为C++11的原因这么慢。。题目的话没什么好说的，简单DP，类似完全背包，注意题目是递减输出，我开始看到递增了，WA了一次

#include<iostream>
#include<vector>
#include<cstring>

using namespace std;

vector<int> primes(int max)
{
	vector<int> res { 2 };
	for (int i = 3; i <= max; i += 2)
	{
		bool is_prime = true;
		for (int p : res)
		{
			if (i % p == 0)
			{
				is_prime = false;
				break;
			}
			if (p * p > i)
				break;
		}
		if (is_prime)
			res.push_back(i);
	}
	return res;
}

int main()
{
	vector<int> res = primes(10000);
	int dp[10001], path[10001];
	memset(dp, 1, sizeof(dp));
	memset(path, 0, sizeof(path));
	dp[0] = 0;
	for (int prime : res)
		for (int i = prime; i <= 10000; i++)
		{
			if (dp[i - prime] + 1 < dp[i])
			{
				dp[i] = dp[i - prime] + 1;
				path[i] = prime;
			}
		}
	int num;
	while (cin >> num)
	{
		if (num == 0 || num == 1)
		{
			cout << 0 << endl;
			continue;
		}
		cout << dp[num] << endl;
		while (num)
		{
			if (path[num] == num)
				cout << num;
			else
				cout << path[num] << " ";
			num -= path[num];
		}
		cout << endl;
	}
	return 0;
}

我去，不信邪把原来的C++11的特性全去掉了，改用旧C++重写了一遍，时间就提升到20ms了，无语。。新特性难道就这么费时间么，老实把C++0x把编译选项去掉了，默默地用老C++写吧。。唉，不与时俱进啊

#include<cstdio>
#include<vector>
#include<cstring>

using namespace std;

vector<int> primes(int max)
{
	vector<int> res;
	res.push_back(2);
	for (int i = 3; i <= max; i += 2)
	{
		bool is_prime = true;
		int p;
		for (vector<int>::iterator it = res.begin(); it != res.end(); it++)
		{
			p = *it;
			if (i % p == 0)
			{
				is_prime = false;
				break;
			}
			if (p * p > i)
				break;
		}
		if (is_prime)
			res.push_back(i);
	}
	return res;
}

int main()
{
	vector<int> res = primes(10000);
	int dp[10001], path[10001];
	memset(dp, 1, sizeof(dp));
	memset(path, 0, sizeof(path));
	dp[0] = 0;
	int prime;
	for (vector<int>::iterator it = res.begin(); it != res.end(); it++)
	{
		prime = *it;
		for (int i = prime; i <= 10000; i++)
		{
			if (dp[i - prime] + 1 < dp[i])
			{
				dp[i] = dp[i - prime] + 1;
				path[i] = prime;
			}
		}
	}
	int num;
	while (scanf("%d", &num) != EOF)
	{
		if (num == 0 || num == 1)
		{
			puts("0");
			continue;
		}
		printf("%d\n", dp[num]);
		while (num)
		{
			if (path[num] == num)
				printf("%d", num);
			else
				printf("%d ", path[num]);
			num -= path[num];
		}
		putchar('\n');
	}
	return 0;
}