You are given an integer array nums and an integer k.
In one operation, you can pick two numbers from the array whose sum equals k and remove them from the array.
Return the maximum number of operations you can perform on the array.
Example 1:
Input: nums = [1,2,3,4], k = 5
Output: 2
Explanation: 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.
Example 2:
Input: nums = [3,1,3,4,3], k = 6
Output: 1
Explanation: Starting with nums = [3,1,3,4,3]:
- Remove the first two 3's, then nums = [1,4,3]
There are no more pairs that sum up to 6, hence a total of 1 operation.
Constraints:
1 <= nums.length <= 105
1 <= nums[i] <= 109
1 <= k <= 109
Solution:
class Solution {
public int maxOperations(int[] nums, int k) {
Map<Integer, Integer> freq = new HashMap();
int count = 0;
for (int i = 0; i < nums.length; i ++) {
int val = nums[i];
int target = k - val;
if (freq.containsKey(target)) {
count ++;
freq.put(target, freq.get(target) - 1);
if (freq.get(target) == 0) {
freq.remove(target);
}
} else {
freq.put(val, freq.getOrDefault(val, 0) + 1);
}
}
return count;
}
}