Swift LeetCode 249. 分组移位字符串

你的问题不是很清楚，但我相信你是在要求对groupStrings函数做出解释.

在你的问题中，你必须找到移位序列.例句:abc -> bcd -> cde ..... -> xyz.

因此，这背后的逻辑是判断每个字符的ASCII个值.因为如果两个字符串形成移位序列，则它们的任何连续字符对的ASCII值之间的差异是相同的.

例如，我们知道abc、bcd、xyz按移位顺序`.

Characters    ASCCI values     Difference from the 1st value

 a b c           97 98 99.          0 1 2
 b c d           98 99 100.         0 1 2
 x y z           120 121 122.       0 1 2

基本上，在您的函数中发生的事情是创建一个字典，其中包含keys个差异和values个字符串.

func groupStrings(_ strings: [String]) -> [[String]] {
        
     var dict = [[Int]: [String]]() // initialize the dictionary
     
        for word in strings {
            var key = [0]
            if word.count > 1 {
                var a = Array(word) //create an array from the charachters of the word
                let pivot = Int(a[0].asciiValue!) - 97 // get the ASCII value of the 1st lestter
                // we substract 97 because for english letters ASCII values start from 97.
                // by substracting 97 we can map the ASCCII of a to 0, b to 1 .... z to 26
            
                for i in 1..<a.count {
                    // calulate the differences between the ASCII values of any consecutive pairs
                    let index = (Int(a[i].asciiValue!) - 97 + 26 - pivot) % 26
                    key.append(index)
                }
            }

            // here check if there is an already a difference sequence in the dictionary
            //if true we append the word to that exsiting key value pair
            //else create a new key value pair
            if var array = dict[key] {
                array.append(word)
                dict[key] = array
            } else {
                dict[key] = [word]
            }
        }
        return dict.keys.compactMap { dict[$0] }
 }