# 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`

``````class Solution {
public:
bool uniqueOccurrences(vector<int>& arr) {
unordered_map<int, int> numCnt;
unordered_set<int> st;
for (int num : arr) ++numCnt[num];
for (auto a : numCnt) {
if (st.count(a.second)) return false;
st.insert(a.second);
}
return true;
}
};
``````

Github 同步地址:

https://github.com/grandyang/leetcode/issues/1207

https://leetcode.com/problems/unique-number-of-occurrences/

https://leetcode.com/problems/unique-number-of-occurrences/discuss/392858/JavaPython-3-4-liner-and-2-liner-Using-Map-and-Set-w-brief-explanation-and-analysis.

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