README_EN.md

953. Verifying an Alien Dictionary

中文文档

Description

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 lexicographicaly 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 (More info).

 

Constraints:

• 1 <= words.length <= 100
• 1 <= words[i].length <= 20
• order.length == 26
• All characters in words[i] and order are English lowercase letters.

Solutions

Python3

class Solution:
    def isAlienSorted(self, words: List[str], order: str) -> bool:
        index = {c: i for i, c in enumerate(order)}
        for i in range(len(words) - 1):
            w1, w2 = words[i], words[i + 1]
            l1, l2 = len(w1), len(w2)
            flag = False
            for j in range(max(l1, l2)):
                i1, i2 = -1 if j >= l1 else index[w1[j]], -1 if j >= l2 else index[w2[j]]
                if i1 > i2:
                    return False
                if i1 < i2:
                    break
        return True

Java

class Solution {
    public boolean isAlienSorted(String[] words, String order) {
        int[] index = new int[26];
        for (int i = 0; i < index.length; ++i) {
            index[order.charAt(i) - 'a'] = i;
        }
        for (int i = 0; i < words.length - 1; ++i) {
            String w1 = words[i];
            String w2 = words[i + 1];
            int l1 = w1.length(), l2 = w2.length();
            for (int j = 0; j < Math.max(l1, l2); ++j) {
                int i1 = j >= l1 ? -1 : index[w1.charAt(j) - 'a'];
                int i2 = j >= l2 ? -1 : index[w2.charAt(j) - 'a'];
                if (i1 > i2) {
                    return false;
                }
                if (i1 < i2) {
                    break;
                }
            }
        }
        return true;
    }
}

C++

class Solution {
public:
    bool isAlienSorted(vector<string> &words, string order) {
        vector<int> index(26);
        for (int i = 0; i < index.size(); ++i)
            index[order[i] - 'a'] = i;
        for (int i = 0; i < words.size() - 1; ++i)
        {
            string w1 = words[i];
            string w2 = words[i + 1];
            int l1 = w1.size(), l2 = w2.size();
            for (int j = 0; j < max(l1, l2); ++j)
            {
                int i1 = j >= l1 ? -1 : index[w1[j] - 'a'];
                int i2 = j >= l2 ? -1 : index[w2[j] - 'a'];
                if (i1 > i2)
                    return false;
                if (i1 < i2)
                    break;
            }
        }
        return true;
    }
};

Go

func isAlienSorted(words []string, order string) bool {
	index := make(map[byte]int)
	for i := range order {
		index[order[i]] = i
	}
	for i := 0; i < len(words)-1; i++ {
		w1, w2 := words[i], words[i+1]
		l1, l2 := len(w1), len(w2)
		flag := true
		for j := 0; j < min(l1, l2) && flag; j++ {
			i1, i2 := index[w1[j]], index[w2[j]]
			if i1 > i2 {
				return false
			}
			if i1 < i2 {
				flag = false
			}
		}
		if flag && l1 > l2 {
			return false
		}
	}
	return true
}

func min(a, b int) int {
	if a < b {
		return a
	}
	return b
}

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