1207. Unique Number of Occurrences #

Problem #

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

Problem Summary #

Given an integer array arr, help count the number of occurrences of each number in the array. If the number of occurrences of each number is unique, return true; otherwise, return false.

Note:

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

Solution Approach #

• Given an array, first count the frequency of each number, then determine whether the same frequency exists in this array.
• Easy problem. First count the frequency of each number in the array, then use a map to determine whether a frequency is duplicated.

Code #

package leetcode

func uniqueOccurrences(arr []int) bool {
	freq, m := map[int]int{}, map[int]bool{}
	for _, v := range arr {
		freq[v]++
	}
	for _, v := range freq {
		if _, ok := m[v]; !ok {
			m[v] = true
		} else {
			return false
		}
	}
	return true
}