我怎么知道HashMap中的所有值都被访问过一次？

Question

Here, I'm trying to find shortestSubstring from a string and i'm not able to find a way of how should i get to know if all the values of hashmap is visited once or not in O(1), or is there any another way to do it?

String mainString = "abacbbdabc";
String targetString = "adc"; 

HashMap will iterate and updating values until it find out all the characters from the targetString ie first substring will be from index 0 to 6

public String findShortestSubstring(String mainString, String targetString) {
        HashMap<Character, Integer> map = new HashMap<>();
        for (int i = 0; i < targetString.length(); i++) {
            map.put(targetString.charAt(i), 1);
        }

        for (int i = 0; i < mainString.length(); i++) {
            if (map.containsKey(mainString.charAt(i))) {
                map.put(mainString.charAt(i), 0);
            }
        }
        return null;
    }

Answer 1

If I do understand properly:

I would use ArrayList. Try to split on single letter every element into list. For example

mainString=skldfjkldfgj; // split it ["s","k","l","d","f","j","k","l","d","f","g","j"]
targetString=dfj;  //split it too ["d","f","j"]

You know dfj is split into 3 elements into ArrayList. If you find first letter of targetString in mainString then check next 2 elements if they matches.