ZOJ-2414

来源：互联网发布：linux wpa supplicant 编辑：程序博客网时间：2024/05/19 04:28

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;elsecout << 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);elseprintf("%d ", path[num]);num -= path[num];}putchar('\n');}return 0;}

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