CODEWITHSUNDEEP
for-loopswift2
Tang
Tang

Reputation: 401

Swift fatal error: Can't form Range with end < start

LeetCode medium 120. Triangle (Dynamic Programming)

Question:

Given a triangle, find the minimum path sum from top to bottom. Each step you may move to adjacent numbers on the row below.

For example, given the following triangle [ [2], [3,4], [6,5,7], [4,1,8,3] ] //The minimum path sum from top to bottom is 11 (i.e., 2 + 3 + 5 + 1 = 11).

//Note:

//Bonus point if you are able to do this using only O(n) extra space, where n is the total number of rows in the triangle.

I always get

fatal error: Can't form Range with end < start

on "for i in (row-1)...0".

Thank you so much! Appreciate your time!

class Solution
    {
        func minimumTotal(triangle: [[Int]]) -> Int
        {


            if triangle.count == 0
            {
                return 0
            }

            if triangle.count == 1
            {
                return triangle[0][0]
            }


            var arr = [Int](count: triangle.last!.count, repeatedValue: 0)
            let row = triangle.count



            for i in (row-1)...0
            {
                let col = triangle[i].count

                for j in 0...col-1
                {
                    if i == row-1
                    {
                        arr[i] = triangle[i][j]
                        continue
                    }

                    arr[j] = min(arr[j], arr[j+1]) + triangle[i][j]

                }
            }

            return arr[0]
        }

    }


    var test1 = Solution()
    //var input = [[10]]
    //var input = [[1],[2,3]]
    var input = [[-1],[2,3],[1,-1,-3]]
    var result = test1.minimumTotal(input)

    print(result)

Upvotes: 0

Views: 3594

Answers (2)

Tang
Tang

Reputation: 401

for in (0...row-1).reverse()

Swift can't read row-1...0

Upvotes: 4

Sahil
Sahil

Reputation: 9226

It's a bad idea to create a range where the start is higher than the end: your code will compile, but it will crash at runtime, so use stride instead of ranage

for i in (row-1).stride(to: 0, by: 1) {  }

Upvotes: 2

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