659. Encode and Decode Strings modify

encode-and-decode-strings/TonyKim9401.java

@@ -1,16 +1,17 @@
 public class Solution {
-    // time complexity: O(n)
-    // space complexity: O(n)
-    Map<Integer, String> encode = new HashMap<>();
+    // Time complexity: O(n)
+    // Space complexity: O(n)
     /*
      * @param strs: a list of strings
      * @return: encodes a list of strings to a single string.
      */
     public String encode(List<String> strs) {
         // write your code here
-        int key = 0;
-        for (String str : strs) encode.put(key++, str);
-        return String.valueOf(key);
+        StringBuilder sb = new StringBuilder();
+        for (String str : strs) {
+            sb.append(str.length()).append("#").append(str);
+        }
+        return sb.toString();
     }
 
     /*
@@ -20,8 +21,14 @@ public String encode(List<String> strs) {
     public List<String> decode(String str) {
         // write your code here
         List<String> output = new ArrayList<>();
-        int decode = 0;
-        while (decode < Integer.valueOf(str)) output.add(encode.get(decode++));
+        int i = 0;
+        while (i < str.length()) {
+            int idx = str.indexOf('#', i);
+            int length = Integer.parseInt(str.substring(i, idx));
+            String s = str.substring(idx + 1, idx + 1 + length);
+            output.add(s);
+            i = idx + 1 + length;
+        }
         return output;
     }
 }