<p>You are given an integer array <code>nums</code> and an integer <code>k</code>.</p>

<p>In one operation, you can pick two numbers from the array whose sum equals <code>k</code> and remove them from the array.</p>

<p>Return <em>the maximum number of operations you can perform on the array</em>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> nums = [1,2,3,4], k = 5
<strong>Output:</strong> 2
<strong>Explanation:</strong> Starting with nums = [1,2,3,4]:
- Remove numbers 1 and 4, then nums = [2,3]
- Remove numbers 2 and 3, then nums = []
There are no more pairs that sum up to 5, hence a total of 2 operations.</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> nums = [3,1,3,4,3], k = 6
<strong>Output:</strong> 1
<strong>Explanation:</strong> Starting with nums = [3,1,3,4,3]:
- Remove the first two 3&#39;s, then nums = [1,4,3]
There are no more pairs that sum up to 6, hence a total of 1 operation.</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= nums.length &lt;= 10<sup>5</sup></code></li>
	<li><code>1 &lt;= nums[i] &lt;= 10<sup>9</sup></code></li>
	<li><code>1 &lt;= k &lt;= 10<sup>9</sup></code></li>
</ul>

class Solution {
public:
    int maxOperations(vector<int>& nums, int k) {
        unordered_map<int,int> freq;
        unordered_map<int,bool> visit;
        for(auto ele:nums){
            freq[ele]++;
        }
        sort(nums.begin(),nums.end());
        int ans=0;
        int n=nums.size();
        for(int i=0;i<n;i++){
            int target=k-nums[i];
            if(target==nums[i]){
                ans+=(freq[target]/2);
                break;
            }
            if(target<nums[i]) break;
            if(visit[nums[i]]) continue;
            visit[nums[i]]=true;
            int s=i+1,e=n-1,mid;
            while(s<=e){
                mid=s+(e-s)/2;
                if(nums[mid]==target){
                    ans+=min(freq[target],freq[nums[i]]);
                    visit[target]=true;
                    break;
                }
                else if(nums[mid]>target){
                    e=mid-1;
                }
                else{
                    s=mid+1;
                }
            }
        }
        return ans;
    }
};
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