求两两之间的最大公约数

 

#include 
     
      #include 
      
       #include 
       
        #include 
        
         using namespace std;typedef long long LL;const int maxn = 5e4 + 10;const int maxm = 1e6 + 10;int A[maxn];int cnt[maxm];int N;int main() {    memset(cnt, 0, sizeof(cnt));    int ans = 0;    int mx = 1;        scanf("%d", &N);    for (int i = 0; i < N; i++) {        scanf("%d", &A[i]);        mx = max(mx, A[i]);        cnt[A[i]]++;    }    sort(A, A + N);    for (int i = N - 1; i ; i--) if (cnt[A[i]] >= 2) {        ans = A[i];        break;    }    bool flag = 0;    for (int i = (mx + 1) / 2; i >= ans; i--) {        int c = 0;        for (int j = i; j <= mx && c < 2; j += i) {            c += cnt[j];        }        if (c >= 2) {            ans = i;        }    }    printf("%d\n", ans);    return 0;}