522. Longest Uncommon Subsequence II

Given a list of strings, you need to find the longest uncommon subsequence among them. The longest uncommon subsequence is defined as the longest subsequence of one of these strings and this subsequence should not be any subsequence of the other strings.

A subsequence is a sequence that can be derived from one sequence by deleting some characters without changing the order of the remaining elements. Trivially, any string is a subsequence of itself and an empty string is a subsequence of any string.

The input will be a list of strings, and the output needs to be the length of the longest uncommon subsequence. If the longest uncommon subsequence doesn't exist, return -1.

Example 1:

Input: "aba", "cdc", "eae"
Output: 3

Note:

1. All the given strings' lengths will not exceed 10.
2. The length of the given list will be in the range of [2, 50].

Approach #1: Simulate. [Java]

class Solution {

    public int findLUSlength(String[] strs) {
        Arrays.sort(strs, new Comparator<String>() {
            public int compare(String o1, String o2) {
                return o2.length() - o1.length();
            }
        });

        Set<String> duplicates = getDuplicates(strs);
        for (int i = 0; i < strs.length; ++i) {
            if (!duplicates.contains(strs[i])) {
                if (i == 0) return strs[0].length();
                for (int j = 0; j < i; ++j) {
                    if (isSubsequence(strs[j], strs[i])) break;
                    if (j == i - 1) return strs[i].length();
                }
            }
        }

        return -1;
    }

    boolean isSubsequence(String a, String b) {
        int i = 0, j = 0;
        while (i < a.length() && j < b.length()) {
            if (a.charAt(i) == b.charAt(j)) ++j;
            ++i;
        }
        return j == b.length();
    }

    Set<String> getDuplicates(String[] strs) {
        Set<String> set = new HashSet<String>();
        Set<String> duplicates = new HashSet<String>();
        for (String str : strs) {
            if (set.contains(str)) duplicates.add(str);
            set.add(str);
        }
        return duplicates;
    }
}

　　

Analysis:

Sort the string in the reverse order. If there is not duplicates in the array, then the longest string is the answer.

But if there are duplicates, and if the longset string is not the answer, then we need to check other strings. But the smaller string can be subsequence of the bigger string. For this reason, we need to check if the string is a subsquence of all the strings bigger than itself. If not, that is the answer.

Reference:

https://leetcode.com/problems/longest-uncommon-subsequence-ii/discuss/99443/Java(15ms)-Sort-%2B-check-subsequence