[swift-users] Compile time exceeded. Anything wrong?

[Greg Power]

What version of Swift are you using, and what exactly do you mean by 'Xcode cannot stop’? It seems like you might be using an older version of Swift, and have hit upon a compiler bug/performance issue that has since been fixed.

This code fails to compile for me in Swift 3.1:

'let dp' should be 'var dp'

With that fixed, the code takes ~10 seconds to compile (which is much longer than I would expect). 

IIRC, the Swift compiler has a hard time with multidimensional arrays (maybe someone else could enlighten us on why that’s the case). Adapting your code to use a single array brings down the compile time to something much more reasonable, although the code becomes somewhat less intuitive:

class Solution {
    
    func rob(nums: [Int]) -> Int {
        
        guard nums.count > 0 else { return 0 }
        
	let stride: Int = 2
        var dp: [Int] = Array.init(repeating: 0, count: nums.count * stride)
        
        dp[0] = 0
        dp[1] = nums[0]
        
        for i in 1 ..< nums.count {
            
            let base = i * stride
            let prevBase = (i - 1) * stride
            dp[base] = max(dp[prevBase], dp[prevBase + 1])
            dp[base + 1] = dp[prevBase] + nums[i]
            
        }
        
        return 0
        
    }
    
}

If you’re using an older version of Swift and are in a position to update - I’d suggest making the change. Otherwise I’d recommend avoiding multidimensional arrays (if possible).

Greg


> On 5 Jun 2017, at 10:32 pm, Hbucius Smith via swift-users <swift-users at swift.org> wrote:
> 
> Hi Swift-Users,
> 
>     when I compiled the code, Xcode cannot stop, I do not know why. It is very strange. Can anyone help ? Here is the code. I am using Xcode 8.1
> 
> class Solution {
> 
>     func rob(nums: [Int]) -> Int {
> 
>         guard nums.count > 0 else { return 0 }
> 
>         let dp = Array.init(repeating: Array.init(repeating: 0, count: nums.count),
> 
>                             count: 2)
> 
>         dp[0][0] = 0
> 
>         dp[0][1] = nums[0]
> 
>         for i in 1 ..< nums.count {
> 
>             dp[i][0] = max(dp[i - 1][0], dp[i - 1][1])
> 
>             dp[i][1] = dp[i - 1][0] + nums[i]
> 
>         }
> 
>         return 0
> 
>     }
> 
> }
> 
> 
> 
> 
> best wishes for you 
> _______________________________________________
> swift-users mailing list
> swift-users at swift.org
> https://lists.swift.org/mailman/listinfo/swift-users

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