根据出现次数的总和以降序对数组进行排序

给定一个未排序的整数数组，其中可能包含重复元素，按其出现的降序对元素进行排序。如果存在多个元素的出现次数总和相同，则较大的元素将排在第一位。
例子：

Input: arr[] = [2, 4, 1, 2, 4, 2, 10]
Output: arr[] = [10, 4, 4, 2, 2, 2, 1]

Explanation:
Here, 2 appears 3 times, 4 appears 2 times, 1 appears 1 time and 10 appears 1 time.
Thus,
Sum of all occurrences of 2 in given array = 2 * 3 = 6,
Sum of all occurrences of 4 = 4 * 2 = 8,
Sum of all occurrences of 10 = 10 * 1 = 10,
Sum of all occurrences of 1 = 1 * 1 = 1.
Therefore sorting the array in descending order based on the above sum = [ 10, 4, 4, 2, 2, 2, 1 ]

Input2: arr[] = [2, 3, 2, 3, 2, 1, 1, 9, 6, 9, 1, 2]
Output2: [9, 9, 2, 2, 2, 2, 6, 3, 3, 1, 1, 1]

方法：

1. 创建一个映射，将元素映射到它的出现，即如果出现一次，则 a 将映射到 a，但如果出现 m 次，则 a 将映射到 a*m。
2. 完成映射后，根据字典的值而不是键按降序对字典进行排序。在平局的情况下，根据值排序。
3. 最后复制最终输出数组中排序的字典键，并根据它们的键值对获得频率，即如果 a 映射到 a*m，则意味着我们需要在输出数组中包含 a, m 次。

下面是上述方法的实现：

Python

# Python3 program to sort elements of
# arr[] in descending order of sum
# of its occurrence
   
def sort_desc(arr):
      
    # to store sum of all
    # occurrences of an elements
    d_sum = {}
  
    # to store count of
    # occurrence of elements
    d_count ={}
  
    # to store final result
    ans = []
  
    # to store maximum sum of occurrence
    mx = 0
       
    # Traverse and calculate sum
    # of occurrence and count of
    # occurrence of elements of arr[]
    for x in arr:
        if x not in d_sum:
            d_sum[x] = x
            d_count[x] = 1
        else:
            d_sum[x] += x
            d_count[x] += 1
              
    # sort d_sum in decreasing order of its value
    l = sorted(d_sum.items(),  
               reverse = True, 
               key = lambda x:(x[1], x[0]))
  
    # store the final result
    for x in l:
        ans += [x[0]] * d_count[x[0]]
          
    return ans
       
# Driver Code
arr = [3, 5, 2, 2, 3, 1, 3, 1]
print(sort_desc(arr))

输出：

[3, 3, 3, 5, 2, 2, 1, 1]

时间复杂度： O(N*log N)。
空间复杂度： O(N)。

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