Description
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:
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| 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.
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Example 2:
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| 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.
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Constraints:
- 1 <= nums.length <= $10^{5}$
- 1 <= nums[i] <= $10^{9}$
- 1 <= k <= $10^{9}$
Solutions
Using hash map to solve.
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| class Solution {
public:
int maxOperations(vector<int>& nums, int k) {
int res = 0;
unordered_map<int, int> u;
for (int x : nums) {
auto it = u.find(k - x);
if (it != u.end() && it->second) {
it->second--;
res++;
} else {
u[x]++;
}
}
return res;
}
}
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