使用stl :: map和stl :: unordered_map对包含大量重复元素的数组数据进行排序

Question

请从geeksforgeeks https://www.geeksforgeeks.org/how-to-sort-a-big-array-with-many-repetitions/查看此问题的解决方案2.它使用stl :: map并说解决方案是O（n + mlogm），它假定stl :: map插入和查找是在O（1）时间。它是否正确？

给定链接中的代码是：

void sort(int arr[], int n) 
{ 
   //1. Create an empty hash table. 
    map<int, int> count; 

    //2. Input array values are stores as key and their 
    //counts are stored as value in hash table. 
    for (int i=0; i<n; i++) 
        count[arr[i]]++; 

    map<int, int>::iterator it; 
    int index = 0; 

    //3. Consider all keys of hash table and sort them. 
    //In std::map, keys are already sorted. 

    //4. Traverse all sorted keys and print every key its value times. 
    for (it=count.begin(); it!=count.end(); ++it) 
    { 
        while(it->second--) 
        arr[index++]=it->first; 
    } 
} 

Answer 1

这只是std::unordered_map的一个错字，其操作平均为O（1）。