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2206 - Divide Array Into Equal Pairs (Easy)

https://leetcode.com/problems/divide-array-into-equal-pairs/

Problem Statement​

You are given an integer array nums consisting of 2 * n integers.

You need to divide nums into n pairs such that:

  • Each element belongs to exactly one pair.
  • The elements present in a pair are equal.

Return true if nums can be divided into n pairs, otherwise return false.

Approach 1: Brute Force​

Count the frequency for each number. If there is a number with odd frequency, then the answer is false. Otherwise, it must be true.

Written by @wingkwong
class Solution {
public:
    bool divideArray(vector<int>& nums) {
        int n = nums.size(), cnt = 0;
        unordered_map<int, int> m;
        // count the frequency for each number
        for (auto x : nums) m[x]++;
        for (auto x : m) {
            // check if it is odd
            if (x.second & 1) {
                return false;
            }
        }
        return true;
    }
};