查找给定数组中唯一的非重复元素

给定的阵列A []选自N(1≤N≤10 ⁵⁾的正整数，任务是找到单个匹配的唯一的数组元素。
注意：保证数组中仅存在一个这样的元素。

例子：

Input: A[] = {1, 1, 2, 3, 3}
Output: 2
Explanation: 
Distinct array elements are {1, 2, 3}. 
Freequency of these elements are {2, 1, 2} respectively.

Input : A[] = {1, 1, 1, 2, 2, 3, 5, 3, 4, 4}
Output : 5

方法：按照以下步骤解决问题

1. 遍历数组
2. 使用无序映射来存储数组元素的频率。
3. 遍历地图，找到频率为1的元素，然后打印该元素。

下面是上述方法的实现：

C++

// C++ implementation of the
// above approach
 
#include 
using namespace std;
 
// Function call to find
// element in A[] with frequency = 1
void CalcUnique(int A[], int N)
{
    // Stores frequency of
    // array elements
    unordered_map freq;
 
    // Traverse the array
    for (int i = 0; i < N; i++) {
 
        // Update frequency of A[i]
        freq[A[i]]++;
    }
 
    // Traverse the Map
    for (int i = 0; i < N; i++) {
 
        // If non-repeating element
        // is found
        if (freq[A[i]] == 1) {
 
            cout << A[i];
            return;
        }
    }
}
 
// Driver Code
int main()
{
    int A[] = { 1, 1, 2, 3, 3 };
    int N = sizeof(A) / sizeof(A[0]);
 
    CalcUnique(A, N);
 
    return 0;
}

Java

// Java implementation of the
// above approach
import java.util.*;
class GFG
{
 
  // Function call to find
  // element in A[] with frequency = 1
  static void CalcUnique(int A[], int N)
  {
    // Stores frequency of
    // array elements
    HashMap freq = new HashMap();
 
    // Traverse the array
    for (int i = 0; i < N; i++)
    {
 
      // Update frequency of A[i]
      if(freq.containsKey(A[i]))
      {
        freq.put(A[i], freq.get(A[i]) + 1);
      }
      else
      {
        freq.put(A[i], 1);
      }
    }
 
    // Traverse the Map
    for (int i = 0; i < N; i++)
    {
 
      // If non-repeating element
      // is found
      if (freq.containsKey(A[i])&&freq.get(A[i]) == 1)
      {
        System.out.print(A[i]);
        return;
      }
    }
  }
 
  // Driver Code
  public static void main(String[] args)
  {
    int A[] = { 1, 1, 2, 3, 3 };
    int N = A.length;
    CalcUnique(A, N);
  }
}
 
// This code is contributed by 29AjayKumar

Python3

# Python 3 implementation of the
# above approach
from collections import defaultdict
 
# Function call to find
# element in A[] with frequency = 1
def CalcUnique(A, N):
 
    # Stores frequency of
    # array elements
    freq = defaultdict(int)
 
    # Traverse the array
    for i in range(N):
 
        # Update frequency of A[i]
        freq[A[i]] += 1
 
    # Traverse the Map
    for i in range(N):
 
        # If non-repeating element
        # is found
        if (freq[A[i]] == 1):
            print(A[i])
            return
 
# Driver Code
if __name__ == "__main__":
    A = [1, 1, 2, 3, 3]
    N = len(A)
    CalcUnique(A, N)
 
    # This code is contributed by chitranayal.

C#

// C# implementation of the
// above approach
using System;
using System.Collections.Generic;
 
public class GFG
{
 
  // Function call to find
  // element in []A with frequency = 1
  static void CalcUnique(int []A, int N)
  {
     
    // Stores frequency of
    // array elements
    Dictionary freq = new Dictionary();
 
    // Traverse the array
    for (int i = 0; i < N; i++)
    {
 
      // Update frequency of A[i]
      if(freq.ContainsKey(A[i]))
      {
        freq[A[i]] = freq[A[i]] + 1;
      }
      else
      {
        freq.Add(A[i], 1);
      }
    }
 
    // Traverse the Map
    for (int i = 0; i < N; i++)
    {
 
      // If non-repeating element
      // is found
      if (freq.ContainsKey(A[i]) && freq[A[i]] == 1)
      {
        Console.Write(A[i]);
        return;
      }
    }
  }
 
  // Driver Code
  public static void Main(String[] args)
  {
    int []A = { 1, 1, 2, 3, 3 };
    int N = A.Length;
    CalcUnique(A, N);
  }
}
 
// This code is contributed by 29AjayKumar

输出：

2

时间复杂度：O(N)
辅助空间：O(N)

另一种方法：使用内置的Python函数：

• 使用Counter()函数计算频率。
• 遍历数组并找到频率为1的元素并进行打印。

下面是实现：

Python3

# Python 3 implementation of the
# above approach
from collections import Counter
 
# Function call to find
# element in A[] with frequency = 1
def CalcUnique(A, N):
 
    # Calculate frequency of
    # all array elements
    freq = Counter(A)
     
    # Traverse the Array
    for i in A:
 
        # If non-repeating element
        # is found
        if (freq[i] == 1):
            print(i)
            return
 
 
# Driver Code
if __name__ == "__main__":
    A = [1, 1, 2, 3, 3]
    N = len(A)
    CalcUnique(A, N)
 
# This code is contributed by vikkycirus

输出：

2

时间复杂度： O(N)

辅助空间： O(N)