953. Verifying an Alien Dictionary

Easy

In an alien language, surprisingly, they also use English lowercase letters, but possibly in a different order. The order of the alphabet is some permutation of lowercase letters.

Given a sequence of words written in the alien language, and the order of the alphabet, return true if and only if the given words are sorted lexicographically in this alien language.

Example 1:

Input: words = ["hello","leetcode"], order = "hlabcdefgijkmnopqrstuvwxyz"
Output: true
Explanation: As 'h' comes before 'l' in this language, then the sequence is sorted.

Example 2:

Input: words = ["word","world","row"], order = "worldabcefghijkmnpqstuvxyz"
Output: false
Explanation: As 'd' comes after 'l' in this language, then words[0] > words[1], hence the sequence is unsorted.

Example 3:

Input: words = ["apple","app"], order = "abcdefghijklmnopqrstuvwxyz"
Output: false
Explanation: The first three characters "app" match, and the second string is shorter (in size.) According to lexicographical rules "apple" > "app", because 'l' > '∅', where '∅' is defined as the blank character which is less than any other character ().

Constraints:

• 1 <= words.length <= 100

• 1 <= words[i].length <= 20

• order.length == 26

• All characters in words[i] and order are English lowercase letters.

解題

func isAlienSorted(words []string, order string) bool {
    m := make(map[byte]int) 
    for i:=0; i<len(order); i++ { // 將字母與 order 做對應
        m[order[i]] = i
    }

    for i:=1; i<len(words); i++ {
    	// 如果 words[i] 沒有大於前一個，則回傳 false
        if !compare(words[i], words[i - 1], m) { return false } 
    }

    return true
}

func compare(w1, w2 string, m map[byte]int) bool {
	for i := 0; i < len(w1) && i < len(w2); i++ {
		if w1[i] != w2[i] {
			if m[w1[i]] > m[w2[i]] {
				return true
			} else {
				return false
			}
		}
	}

	return len(w1) >= len(w2) // 字母都相同時，長度較短的應該排在前面
}