코딩테스트##007 OddOccurrencesInArray

A non-empty array A consisting of N integers is given. The array contains an odd number of elements, and each element of the array can be paired with another element that has the same value, except for one element that is left unpaired.

For example, in array A such that:

A[0] = 9 A[1] = 3 A[2] = 9
A[3] = 3 A[4] = 9 A[5] = 7
A[6] = 9
the elements at indexes 0 and 2 have value 9,
the elements at indexes 1 and 3 have value 3,
the elements at indexes 4 and 6 have value 9,
the element at index 5 has value 7 and is unpaired.
Write a function:

class Solution { public int solution(int[] A); }

that, given an array A consisting of N integers fulfilling the above conditions, returns the value of the unpaired element.

For example, given array A such that:

A[0] = 9 A[1] = 3 A[2] = 9
A[3] = 3 A[4] = 9 A[5] = 7
A[6] = 9
the function should return 7, as explained in the example above.

Write an efficient algorithm for the following assumptions:

• N is an odd integer within the range [1..1,000,000];
• each element of array A is an integer within the range [1..1,000,000,000];
• all but one of the values in A occur an even number of times.

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나의 풀이

import java.util.*;

class Solution {
    public int solution(int[] A) {

        Map<Integer, Integer> map = new HashMap<>();
        
        for (int a : A) {
            map.put(a, map.getOrDefault(a, 0) + 1);
        }

        for (int key : map.keySet()) {
            if (map.get(key) % 2 != 0) {
                return key;
            }
        }
        
        return 0;
    }
}

check 1 : 배열에 중복된 숫자가 있는지 확인

Map의 getOrDefault 함수 활용

check 2 : 홀수 번 등장하는 숫자 확인

1번만 등장하는게 아니라 홀수 번 등장하는 숫자를 찾는 것이므로 map의 value가 홀수인 것 찾기