feat: solve encode and decode strings

encode-and-decode-strings/GangBean.java

@@ -0,0 +1,52 @@
+import java.util.*;
+
+public class Codec {
+    /**
+    1. complexity:
+    - time: O(N * L), where N is the length of strs, L is maximum length of each word in strs
+    - space: O(N * L)
+    */
+
+    // Encodes a list of strings to a single string.
+    public String encode(List<String> strs) {
+        // 필요한 정보: 전체 원본 문자열, 각 단어의 위치와 길이
+        StringBuilder origin = new StringBuilder();
+        StringJoiner meta = new StringJoiner("/");
+        StringJoiner encoded = new StringJoiner(";");
+        int startIdx = 0;
+        for (String word: strs) { // O(N)
+            origin.append(word);
+            meta.add(String.format("(%d,%d)", startIdx, word.length()));
+            startIdx += word.length();
+        }
+
+        encoded.add(origin.toString()).add(meta.toString());
+        return encoded.toString();
+    }
+
+    // Decodes a single string to a list of strings.
+    public List<String> decode(String s) {
+        List<String> ret = new ArrayList<>();
+        int delimeterIdx = s.lastIndexOf(";"); // O(N * L)
+        String origin = s.substring(0, delimeterIdx); // O(N * L)
+        String meta = s.substring(delimeterIdx+1); // O(N * L)
+        String[] wordInfos = meta.split("/");
+        for (String wordInfo: wordInfos) { // O(N)
+            delimeterIdx = wordInfo.indexOf(","); // O(1)
+            int length = Integer.parseInt(wordInfo.substring(delimeterIdx+1, wordInfo.length() - 1)); // O(1)
+            String word = "";
+            if (length > 0) {
+                int startIdx = Integer.parseInt(wordInfo.substring(1, delimeterIdx));
+                word = origin.substring(startIdx, startIdx + length);
+            }
+            ret.add(word);
+        }
+        return ret;
+    }
+}
+
+// Your Codec object will be instantiated and called as such:
+// Codec codec = new Codec();
+// codec.decode(codec.encode(strs));
+
+