243. Shortest Word Distance

https://leetcode.com/problems/shortest-word-distance/description/

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.

Note:
You may assume that word1 does not equal to word2, and word1 and word2 are both in the list.

Sol :

Algorithm

We can greatly improve on the brute-force approach by keeping two indices i1 and i2 where we store the most recent locations of word1 and word2. Each time we find a new occurrence of one of the words, we do not need to search the entire array for the other word, since we already have the index of its most recent occurrence.

Complexity Analysis

The time complexity is O(n). This problem is inherently linear; we cannot do better than O(n)O(n) because at the very least, we have to read the entire input.

Space complexity is O(1), since no additional space is allocated.

public class Solution {
    public int shortestDistance(String[] words, String word1, String word2) {
        int i1 = -1, i2 = -1;
        int minDis = words.length;
        int curDis;
        for(int i = 0; i < words.length; i++){
            if (words[i].equals(word1)){
                i1 = i;
            } else if (words[i].equals(word2)){
                i2 = i;
            }
                if (i1 != -1 && i2 != -1){
                    minDis = Math.min(minDis, Math.abs(i1-i2));
                }
        }
        
        return minDis;
        
    }
}