poj 2262 Goldbach's Conjecture
Time Limit: 1000MS | Memory Limit: 65536K | |
Total Submissions: 39353 | Accepted: 15077 |
Description
Every even number greater than 4 can be
written as the sum of two odd prime numbers.
For example:
8 = 3 + 5. Both 3 and 5 are odd prime numbers.
20 = 3 + 17 = 7 + 13.
42 = 5 + 37 = 11 + 31 = 13 + 29 = 19 + 23.
Today it is still unproven whether the conjecture is right. (Oh wait, I have the proof of course, but it is too long to write it on the margin of this page.)
Anyway, your task is now to verify Goldbach‘s conjecture for all even numbers less than a million.
Input
Each test case consists of one even integer n with 6 <= n < 1000000.
Input will be terminated by a value of 0 for n.
Output
Sample Input
8 20 42 0
Sample Output
8 = 3 + 5 20 = 3 + 17 42 = 5 + 37
Source
1 #include<cstdio> 2 #include<algorithm> 3 #include<iostream> 4 #include<string> 5 #include<cstring> 6 #include<vector> 7 using namespace std; 8 #define max 1000000 9 int prime[max+5]; 10 bool vis[max+5]; 11 void get_prime(int n){ 12 memset(vis,false,sizeof(vis)); 13 vis[0]=vis[1]=true; 14 int i=2,index=0; 15 for(;i<=n;i++){ 16 if(!vis[i]){ 17 prime[index++]=i; 18 //vis[i]=false; 19 } 20 int j=0; 21 for(;j<index&&prime[j]*i<=n;j++){//???? 22 vis[prime[j]*i]=true; 23 if(!(i%prime[j])) 24 break; 25 } 26 } 27 } 28 int main(){ 29 int n; 30 get_prime(max); 31 while(cin>>n&&n){ 32 int i=3,half=n/2; 33 for(;i<=half;i+=2){//等号一定要取到,存在数等于两个相同质数之和的 34 if(!vis[i]&&!vis[n-i]){ 35 break; 36 } 37 } 38 if(i>half) 39 cout<<"Goldbach‘s conjecture is wrong."<<endl; 40 else 41 cout<<n<<" = "<<i<<" + "<<n-i<<endl; 42 } 43 return 0; 44 }
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