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// @Title: 三数之和 (3Sum)
// @Author: 15816537946@163.com
// @Date: 2022-03-17 17:29:05
// @Runtime: 28 ms
// @Memory: 7.3 MB
func threeSum(nums []int) [][]int {
    nLen := len(nums)
    if nLen < 3 {
        return nil
    }

    sort.Ints(nums)
    
    ret := make([][]int, 0)

    for i := range nums {
        if i > 0 && nums[i] == nums[i-1] {
            continue
        }

        lo, hi := i+1, nLen-1
        for lo < hi {
            sum := nums[i] + nums[lo] + nums[hi] 
            if sum == 0 {
                ret = append(ret,[]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 sum > 0 {
                hi--
            } else {
                lo++
            }
        }
    }
    return ret
}