953. Verifying an Alien Dictionary

/*
Time Complexity: O(M * N) or O(Total number of chars in words array)
Space Complexity: O(1) or O(26)

M = Average length of each word
N = Number of words
*/
class Solution {
    public boolean isAlienSorted(String[] words, String order) throws IllegalArgumentException {
        if (words == null || order == null || order.length() != 26) {
            throw new IllegalArgumentException("Invalid input");
        }
        if (words.length < 2) {
            return true;
        }

        int[] orderDict = new int[26];
        for (int i = 0; i < order.length(); i++) {
            orderDict[order.charAt(i) - 'a'] = i;
        }

        for (int i = 1; i < words.length; i++) {
            if (compare(words[i-1], words[i], orderDict) > 0) {
                return false;
            }
        }

        return true;
    }

    private int compare(String A, String B, int[] orderDict) {
        int lenA = A.length();
        int lenB = B.length();
        for (int i = 0; i < Math.min(lenA, lenB); i++) {
            if (A.charAt(i) != B.charAt(i)) {
                return orderDict[A.charAt(i)-'a'] - orderDict[B.charAt(i)-'a'];
            }
        }
        return lenA - lenB;
    }
}