easy/2341. Maximum Number of Pairs in Array.md · hugh_sun/leetcode

**[2341. Maximum Number of Pairs in Array](https://leetcode.com/contest/weekly-contest-302/problems/maximum-number-of-pairs-in-array/)**

You are given a 0-indexed integer array nums. In one operation, you may do the following:

* Choose two integers in nums that are equal.
* Remove both integers from nums, forming a pair.

The operation is done on nums as many times as possible.

Return a 0-indexed integer array answer of size 2 where answer[0] is the number of pairs that are formed and answer[1] is the number of leftover integers in nums after doing the operation as many times as possible..

**Example 1:**
```
Input: nums = [1,3,2,1,3,2,2]
Output: [3,1]
Explanation:
Form a pair with nums[0] and nums[3] and remove them from nums. Now, nums = [3,2,3,2,2].
Form a pair with nums[0] and nums[2] and remove them from nums. Now, nums = [2,2,2].
Form a pair with nums[0] and nums[1] and remove them from nums. Now, nums = [2].
No more pairs can be formed. A total of 3 pairs have been formed, and there is 1 number leftover in nums.
```

**Example 2:**
```
Input: nums = [1,1]
Output: [1,0]
Explanation: Form a pair with nums[0] and nums[1] and remove them from nums. Now, nums = [].
No more pairs can be formed. A total of 1 pair has been formed, and there are 0 numbers leftover in nums.
```

**Example 3:**
```
Input: nums = [0]
Output: [0,1]
Explanation: No pairs can be formed, and there is 1 number leftover in nums.
```

**Constraints:**

* 1 <= nums.length <= 100
* 0 <= nums[i] <= 100

**Solution:**

Runtime: 1 ms<br/>
Memory Usage: 40.9 MB

```java
class Solution {
    public int[] numberOfPairs(int[] nums) {
        Map<Integer, Integer>  map= new HashMap<>();
        int numsOfPair = 0;
        for(int i = 0; i < nums.length; i++) {
            if(map.containsKey(nums[i])) {
                numsOfPair++;
                int m = map.get(nums[i]) - 1;
                if(m == 0) {
                    map.remove(nums[i]);
                } else {
                    map.put(nums[i], m);
                }
                
            } else {
                map.put(nums[i], 1);
            }
        }
        return new int[]{numsOfPair, map.size()};
    }
}

```

hugh_sun/leetcode

About

Releases

Contributors

Language(Optional)

Activities