找出在一个数组中出现n/2次的数

int main() 
{ 
    int a[] = {1 , 2 , 3, 1 }; 
    int n = sizeof (a )/ sizeof(a[0]); 

    int i; 
    for ( i = 0; i < n; i++ ) 
    { 
        if ( a[i] == a[(i+1)%n ] || a[i] == a[(i+2)%n] ) 
        { 
            printf("%d ", a[i] ); 
            break; 
        } 
    } 
    getch(); 
    return 0; 
}