953.py

'''
953. Verifying an Alien Dictionary
https://leetcode.com/problems/verifying-an-alien-dictionary/

Hi, here's your problem today. This problem was recently asked by Apple:

Given an array with n objects colored red, white or blue, sort them in-place so that objects of the same color are adjacent, with the colors in the order red, white and blue.

Here, we will use the integers 0, 1, and 2 to represent the color red, white, and blue respectively.

Note: You are not suppose to use the library’s sort function for this problem.

Can you do this in a single pass?

Example:
Input: [2,0,2,1,1,0]
Output: [0,0,1,1,2,2]
'''
from typing import *

class Solution:
    def isAlienSorted(self, words: List[str], order: str) -> bool:
        order_index = {c: i for i, c in enumerate(order)}

        for i in range(len(words) - 1):
            word1 = words[i]
            word2 = words[i+1]

            # Find the first difference word1[k] != word2[k].
            for k in range(min(len(word1), len(word2))):
                # If they compare badly, it's not sorted.
                if word1[k] != word2[k]:
                    if order_index[word1[k]] > order_index[word2[k]]:
                        return False
                    break
            else:
                # If we didn't find a first difference, the
                # words are like ("app", "apple").
                if len(word1) > len(word2):
                    return False

        return True

print(Solution().isAlienSorted(["hello","leetcode"], "hlabcdefgijkmnopqrstuvwxyz"))
#True
print(Solution().isAlienSorted(["word","world","row"], "worldabcefghijkmnpqstuvxyz"))
#False
print(Solution().isAlienSorted(["apple","app"], "abcdefghijklmnopqrstuvwxyz"))
#False