func threeSum(nums []int) [][]int {
if len(nums) < 3 {
return nil
}
// 排序
quickSort(nums, 0, len(nums)-1)
ans := make([][]int, 0)
for i := 0; i < len(nums)-2; i++ {
// 如果当前数字大于0,则三数之和一定大于0,所以结束循环
if nums[i] > 0 {
break
}
// 去重
if i > 0 && nums[i] == nums[i-1] {
continue
}
// 双指针
left, right := i+1, len(nums)-1
for left < right {
sum := nums[i] + nums[left] + nums[right]
switch {
case sum == 0:
ans = append(ans, []int{nums[i], nums[left], nums[right]})
// 去重
for left < right && nums[left] == nums[left+1] {
left++
}
// 去重
for left < right && nums[right] == nums[right-1] {
right--
}
left++
right--
case sum < 0:
left++
case sum > 0:
right--
}
}
}
return ans
}
func quickSort(nums []int, left, right int) {
if left < right {
pivot := partition(nums, left, right)
quickSort(nums, left, pivot-1)
quickSort(nums, pivot+1, right)
}
}
func partition(nums []int, left, right int) int {
pivot := nums[left]
for left < right {
for left < right && nums[right] >= pivot {
right--
}
nums[left] = nums[right]
for left < right && nums[left] <= pivot {
left++
}
nums[right] = nums[left]
}
nums[left] = pivot
return left
}