Leetcode - Shortest Word Distance

Given a list of words and two words word1 and word2, return the shortest distance between these two words in the list.

For example,
Assume that words = ["practice", "makes", "perfect", "coding", "makes"].

Given word1 = “coding”, word2 = “practice”, return 3.
Given word1 = "makes", word2 = "coding", return 1.

public class Solution {
    public int shortestDistance(String[] words, String word1, String word2) {
        if (words == null) return -1;
        int idx1 = -1, idx2 = -1;
        int diff = words.length;
        for (int i = 0; i < words.length; i++) {
            if (words[i].equals(word1)) {
                idx1 = i;
                if (idx2 != -1) 
                    diff = Math.min(diff, idx1 - idx2);
            } else if (words[i].equals(word2)) {
                idx2 = i;
                if (idx1 != -1) 
                    diff = Math.min(diff, idx2 - idx1);
            }
        }
        return diff;
    }
}