1207. Unique Number of Occurrences

Given an array of integers arr, write a function that returns true if and only if the number of occurrences of each value in the array is unique.

 

Example 1:

Input: arr = [1,2,2,1,1,3]
Output: true
Explanation: The value 1 has 3 occurrences, 2 has 2 and 3 has 1. No two values have the same number of occurrences.
Example 2:

Input: arr = [1,2]
Output: false
Example 3:

Input: arr = [-3,0,1,-3,1,1,1,-3,10,0]
Output: true
 

Constraints:

1 <= arr.length <= 1000
-1000 <= arr[i] <= 1000

这题题意是让我们求出是否给定的数组中，每个数字出现的次数都是唯一的。

我这里先排序，然后遍历一次，当数字发生变更的时候，记录下前一串相同数字的出现次数，当次数存在的时候，直接返回false即可。

需要注意的是，最后还需要判断一下，因为最后一个数不会出发判断的逻辑，需要额外判断。

class UniqueNumberofOccurrences : public Solution {
public:
    void Exec() {

    }
    bool uniqueOccurrences(vector<int>& arr) {
        std::sort(arr.begin(), arr.end());
        std::set<int> occurrences;

        int count = 0, prev = 0;
        for (int i = 0; i < arr.size(); i++) {
            if (i == 0 || arr[i] == prev) {
                count++;
            } else {
                auto it = occurrences.find(count);
                if (it != occurrences.end()) {
                    return false;
                }
                occurrences.insert(count);
                count = 1;
            }
            prev = arr[i];
        }
        return occurrences.find(count) == occurrences.end();
    }
};