1207. Unique Number of Occurrences*
https://leetcode.com/problems/unique-number-of-occurrences/
题目描述
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
C++ 实现 1
判断每个元素出现的个数是不是 unique 的.
使用两个哈希表, 一个记录每个元素的个数, 另一个判断是否出现的个数是 unique 的.
class Solution {
public:
bool uniqueOccurrences(vector<int>& arr) {
unordered_map<int, int> record;
unordered_set<int> nums;
for (auto &c : arr)
record[c] ++;
for (auto &p : record) {
if (nums.count(p.second)) return false;
nums.insert(p.second);
}
return true;
}
};
C++ 实现 2
或者这样写, 来自 LeetCode Submission
class Solution {
public:
bool uniqueOccurrences(vector<int>& arr) {
unordered_map<int, int> m;
unordered_set<int> s;
for (auto n : arr) ++m[n];
for (auto& p : m) s.insert(p.second);
return m.size() == s.size();
}
};
