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sum.go
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/
sum.go
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package sum
import (
"sort"
"github.com/catorpilor/leetcode/utils"
)
func maxKSumOps(nums []int, k int) int {
return useTwoPointers(nums, k)
}
// useTwoPointers time complexity O(N*log(N)), space complexity O(1)
func useTwoPointers(nums []int, k int) int {
n := len(nums)
sort.Ints(nums)
l, r := 0, n-1
var ans int
for l < r {
cs := nums[l] + nums[r]
if cs == k {
ans++
l++
r--
} else if cs < k {
l++
} else {
r--
}
}
return ans
}
// useHashmap time complexity O(N), space complexity O(N)
func useHashmap(nums []int, k int) int {
n := len(nums)
set := make(map[int]int, n)
for _, num := range nums {
set[num]++
}
var ans int
for num, v := range set {
if k-num == num {
ans += v / 2
} else if set[k-num] != 0 {
cm := utils.Min(v, set[k-num])
ans += cm
set[num] -= cm
set[k-num] -= cm
}
}
return ans
}