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4sum.go
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4sum.go
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// https://leetcode.com/problems/4sum
package leetcode
import "sort"
func fourSum(nums []int, target int) [][]int {
if len(nums) < 4 {
return [][]int{}
}
sort.Ints(nums)
var result [][]int
for i := 0; i <= len(nums)-4; i++ {
if i > 0 && nums[i] == nums[i-1] { // avoid duplicate
continue
}
a := threeSum(nums[i+1:], target-nums[i])
for _, r := range a {
b := []int{nums[i]}
b = append(b, r...)
result = append(result, b)
}
}
return result
}
func threeSum(nums []int, target int) [][]int {
var result [][]int
for i := 0; i < len(nums)-2; i++ {
if i == 0 || (i > 0 && nums[i] != nums[i-1]) {
lo := i + 1
hi := len(nums) - 1
sum := target - nums[i]
for lo < hi {
if nums[lo]+nums[hi] == sum {
result = append(result, []int{nums[i], nums[lo], nums[hi]})
for lo < hi && nums[lo] == nums[lo+1] {
lo++
}
for lo < hi && nums[hi] == nums[hi-1] {
hi--
}
lo++
hi--
} else if nums[lo]+nums[hi] < sum {
lo++
} else {
hi--
}
}
}
}
return result
}