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
這道題給了一個整型數組，問每個數字出現的次數都否都不同。對於一道 Easy 的題目來說，沒有太大的難度，就是用個 HashMap 來統計每個數字出現的次數，然后再用個 HashSet 來判斷某個次數是否之前出現過了，若出現過了，則返回 false，否則最終返回 true 即可，參見代碼如下：
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
參考資料：
https://leetcode.com/problems/unique-number-of-occurrences/