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;
}

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