PKU 2262 - Goldbach's Conjecture (数论)
题意
把一个大于二的偶数分解成两个素数和
思路
先筛出素数
代码
#include <stack>
#include <cstdio>
#include <list>
#include <set>
#include <iostream>
#include <string>
#include <vector>
#include <queue>
#include <functional>
#include <cstring>
#include <algorithm>
#include <cctype>
#include <string>
#include <map>
#include <cmath>
using namespace std;
#define LL long long
#define ULL unsigned long long
#define SZ(x) (int)x.size()
#define Lowbit(x) ((x) & (-x))
#define MP(a, b) make_pair(a, b)
#define MS(arr, num) memset(arr, num, sizeof(arr))
#define PB push_back
#define X first
#define Y second
#define ROP freopen("input.txt", "r", stdin);
#define MID(a, b) (a + ((b - a) >> 1))
#define LC rt << 1, l, mid
#define RC rt << 1|1, mid + 1, r
#define LRT rt << 1
#define RRT rt << 1|1
#define BitCount(x) __builtin_popcount(x)
#define BitCountll(x) __builtin_popcountll(x)
#define LeftPos(x) 32 - __builtin_clz(x) - 1
#define LeftPosll(x) 64 - __builtin_clzll(x) - 1
const double PI = acos(-1.0);
const int INF = 0x3f3f3f3f;
const double eps = 1e-8;
const int MAXN = 1e6 + 10;
const int MOD = 1000007;
const int dir[][2] = { {1, 0}, {0, 1} };
int cases = 0;
typedef pair<int, int> pii;
typedef vector<int>::iterator viti;
typedef vector<pii>::iterator vitii;
int vis[MAXN], n;
void get_prime()
{
int limit = (int)sqrt(MAXN + 0.5);
for (int i = 2; i <= limit; i++) if (!vis[i])
for (int j = i*i; j <= MAXN; j += i) vis[j] = 1;
}
int main()
{
get_prime();
while (scanf("%d", &n), n)
{
for (int i = 2; i <= (n>>1); i++)
if (!vis[i] && !vis[n-i])
{
printf("%d = %d + %d\n", n, i, n-i);
break;
}
}
return 0;
}