swift - 我的 Swift 代码出现错误无法形成上限 < 下限的范围

Question

我尝试在 leetcode site 中运行我的代码.在 XCode 中，这段代码编译成功。但是在 leetcode 中是错误的:

Fatal error: Can't form range with upperbound < lowerbound

任务描述:

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.

我对这个任务的解决方案是:

class Solution {
    func threeSum(_ nums: [Int]) -> [[Int]] {
        var arr: [[Int]] = []

        var fIndex  = 0
        var sIndex  = 1
        var tIndex  = 2

        for i in fIndex..<nums.count-2 {
            for n in sIndex..<nums.count-1 {
                for z in tIndex..<nums.count {
                    let sum = nums[i] + nums[n] + nums[z]

                    if sum == 0 {
                        arr.append([nums[i], nums[n], nums[z]])
                    }
                }

                sIndex += 1
                tIndex += 1
            }

            fIndex += 1
        }

        return arr
    }
}
// delete this in leetcode site
let threeNums = [-1, 0, 1, 2, -1, -4]
let sol = Solution()
print(sol.threeSum(threeNums))

我的代码哪里出了问题？

Answer 1

假设代码的所有其他部分都有效，您只需要在循环之前检查输入数组的元素是否少于 3 个:

class Solution {
    func threeSum(_ nums: [Int]) -> [[Int]] {
        var arr: [[Int]] = []

        var fIndex  = 0
        var sIndex  = 1
        var tIndex  = 2

        if nums.count < 3 { return [] } // if there is less than 3 elements, there can't be any triplets

        for i in fIndex..<nums.count-2 {
            ...

如果没有检查，当 nums 只有一个元素时，您的代码将失败，而 enums.count - 2 将是 -1.