threeSum_0

//找出数组中三个数相加为0，返回存在的组数
//输入指正*A,长度为size，返回*B和长度num
int threeSum_0(int *A,int size,int *B,int &num)
{
    vector<int> temp(A, A + size); //使用vector操作数据
    sort(temp.begin(),temp.end());//sort 
    //夹逼
    auto last = temp.end();
    int  *p = new int[30];//p为临时数组，大小自己设置
    for (auto a = temp.begin(); a <prev(last,2); a++){
        auto b = next(a);
        auto c = prev(last);
        while (b < c){
            if (*a + *b + *c > 0)
                --c;
            else if (*a + *b + *c < 0)
                ++b;
            else{
                *(p++) = *a;
                *(p++) = *b;
                *(p++) = *c;
                num = num + 3;
                ++b;
                --c;
            }    
        }
    }
    p = p - num;
    for (int i = 0; i < num; i++)
        B[i] = p[i];
    delete[] p;
    return  num/3; //符合条件的组数
}