15. 3Sum

Description

Given an array nums of n integers, are there elements a, b, c in nums such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero.

Note:

The solution set must not contain duplicate triplets.

Example:

Given array nums = [-1, 0, 1, 2, -1, -4],

A solution set is:
[
  [-1, 0, 1],
  [-1, -1, 2]
]

Tags: Array, Two Pointers

题意

从数组中找出所有三个和为 0 的元素构成的非重复序列

题解

思路1

我们可以把数组先做下排序,然后遍历这个排序数组,用两个指针分别指向当前元素的下一个和数组尾部,判断三者的和与 0 的大小来移动两个指针,其中细节操作就是优化和去重。

func threeSum(nums []int) [][]int {
    ans := [][]int{}
    if len(nums) <= 2 {
        return ans
    }

    //    排序
    sort.Ints(nums)

    for i := 0; i < len(nums)-2; i++ {
        if i == 0 || (i > 0 && nums[i] != nums[i-1]) {
            low, high, sum := i+1, len(nums)-1, 0-nums[i]
            for low < high {
                //    和为0的时候
                if nums[low]+nums[high] == sum {
                    ans = append(ans, []int{nums[i], nums[low], nums[high]})
                    //    排除;连续相等的数
                    for low < high && nums[low] == nums[low+1] {
                        low++
                    }
                    for low < high && nums[high] == nums[high-1] {
                        high--
                    }
                    low++
                    high--
                } else if nums[low]+nums[high] < sum {
                    low++
                } else {
                    high--
                }

            }

        }
    }
    return ans
}

思路2

思路2 ```go

```

结语

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