【LeetCode 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]
]
思路:
题目要求找出所有三个和为 0 的元素构成的非重复三元数组。首先对数组进行一个排序,排序后循环先取一个数固定,用双指针分别指向当前元素的下一个和数组尾数,判断三者的和与 0 的大小来移动两个指针,并进行去重。
Kotlin代码实现:
fun threeSum(nums: IntArray): List<List<Int>> {
val answer: ArrayList<List<Int>> = ArrayList()
val length = nums.size
if (length < 3) return answer
Arrays.sort(nums)
for (i in 0 until length) {
if (nums[i] > 0) break
if (i > 0 && nums[i] == nums[i - 1]) continue
var left = i + 1
var right = length - 1
while (left < right) {
val sum = nums[i] + nums[left] + nums[right]
if (sum == 0) {
answer.add(listOf(nums[i], nums[left], nums[right]))
while (left < right && nums[left] == nums[left + 1]) left++
while (left < right && nums[right] == nums[right - 1]) right--
left++
right--
} else if (sum < 0){
left++
} else if (sum > 0){
right--
}
}
}
return answer
}