0001 template <typename T> //对各自有序的[lo,mi)和[mi,hi)做归并
0002 void Vector<T>::merge(Rank lo, Rank mi, Rank hi) { //lo < mi < hi
0003    Rank s = 0; T* S = _elem + lo; //就地归并至序列S[0,hi-lo)
0004    Rank a = 0, la = mi-lo; T* A = new T[la]; //A[0,la)复制自
0005    for (Rank i = 0; i < la; i++) A[i] = S[i]; //S的前缀
0006    Rank b = 0, lb = hi-mi; T* B = S + la; //B[0,lb)就是S的后缀
0007    while ((a < la) && (b < lb)) //反复地比较A、B的首元素
0008       S[s++] = (A[a] <= B[b]) ? A[a++] : B[b++]; //小者优先归入S
0009    while (a < la) //若B先耗尽，则还需将A残余的后缀归入S
0010       S[s++] = A[a++]; //反之若A先耗尽，因B残余的后缀已在S中，故无需处理
0011    delete[] A; //new和delete很耗时，如何减少？
0012 } //merge