c_cpp 给出一个大小为N的数组，其内容为0,1或2（当然重复）。一次性对数组进行排序。

Posted 2021-05-14

void sort_array_containing_0_1_2_only(vector<int> &A) {
    if(A.empty()) return;
    int i = 0, j = A.size()-1;
    int k = 0;
    while(k <= j) {   // gist, should <= j
        if(A[k] == 1) k++;
        else if(A[k] == 0) 
            swap(A[i++], A[k++]); // cannot forget to update k!!!
        else // A[k] == 2
            swap(A[j--], A[k]); // no ++?
    }
}

void sort_array_containing_012(vector<int>& A) {
    if(A.empty()) return;
    int edge_of_0 = 0;
    int edge_of_2 = A.size() - 1;
    int i = 0;
    while(edge_of_0 <= edge_of_2) {
        if(A[i] == 1)
            i++;
        else if(A[i] == 0)
            swap(A[edge_of_0++], A[i++]);
        else swap(A[edge_of_2--], A[i]); // no ++?
    }
}