1207. Unique Number of Occurrences.md

1207. Unique Number of Occurrences

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leetcode-cn Daily Challenge on October 28th, 2020.

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Difficulty : Easy

Related Topics : HashTable

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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

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Solution

• mine
  • Java
    • use map to collection the value. Runtime: 2 ms, faster than 88.01%, Memory Usage: 35.6 MB, less than 100.00%

      public boolean uniqueOccurrences(int[] arr) {
          Map<Integer, Integer> map = new HashMap<>();
          for (int i = 0; i < arr.length; i++) {
              int t = arr[i];
              if (map.containsKey(t)) {
                  map.put(t, map.get(t) + 1);
              } else {
                  map.put(t, 1);
              }
          }
          List<Integer> list = new ArrayList<>();
          Iterator<Map.Entry<Integer, Integer>> iterator = map.entrySet().iterator();
          while (iterator.hasNext()) {
              int v = iterator.next().getValue();
              if (list.contains(v)) {
                  return false;
              }else{
                  list.add(v);
              }
          }
          return true;
      } 
      

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• the most votes

• Runtime: 2 ms, faster than 88.01%, Memory Usage: 36 MB, less than 100.00%

  public boolean uniqueOccurrences(int[] arr) {
      Map<Integer, Integer> count = new HashMap<>();
      for (int a : arr)
          count.put(a, 1 + count.getOrDefault(a, 0));
      return count.size() == new HashSet<>(count.values()).size();
  }
  

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