October 30, 2019

271. Encode and Decode Strings

Referred to this post for why this works:
“aa2/bb” will be encoded as “6/aa2/bb”. When decoding, it finds a string of length of 6 which includes “aa2/bb” so it won’t be able to read the “2/” as you might be thinking of.

Time = O(n), space = O(1)

public class Codec {

    // Encodes a list of strings to a single string.
    public String encode(List<String> strs) {
        StringBuilder sb = new StringBuilder();
        for (String str : strs) {
            sb.append(str.length());
            sb.append("/");
            sb.append(str);
        }
        return sb.toString();
    }

    // Decodes a single string to a list of strings.
    public List<String> decode(String s) {
        List<String> strs = new ArrayList<>();
        int i = 0;
        while (i < s.length()) {
            int slash = s.indexOf("/", i);
            int size = Integer.valueOf(s.substring(i, slash));
            i = slash + size + 1;
            strs.add(s.substring(slash + 1, i));
        }
        return strs;
    }
}

// Your Codec object will be instantiated and called as such:
// Codec codec = new Codec();
// codec.decode(codec.encode(strs));