Update 269_Alien_Dictionary.java

Author: seanprashad

Topological Sort/269_Alien_Dictionary.java

@@ -1,27 +1,32 @@
 class Solution {
     public String alienOrder(String[] words) {
-        Map<Character, List<Character>> adjList = new HashMap<>();
-        Map<Character, Integer> inorderMap = new HashMap<>();
+        if (words == null || words.length == 0) {
+            return "";
+        }
+
+        Map<Character, List<Character>> graph = new HashMap<>();
+        Map<Character, Integer> inorder = new HashMap<>();
 
-        for (String word : words) {
-            for (char c : word.toCharArray()) {
-                adjList.putIfAbsent(c, new ArrayList<>());
-                inorderMap.putIfAbsent(c, 0);
+        for (String w : words) {
+            for (char c : w.toCharArray()) {
+                graph.putIfAbsent(c, new ArrayList<>());
+                inorder.putIfAbsent(c, 0);
             }
         }
 
         for (int i = 0; i < words.length - 1; i++) {
-            String word1 = words[i];
-            String word2 = words[i + 1];
+            String word1 = words[i], word2 = words[i + 1];
 
             if (word1.length() > word2.length() && word1.startsWith(word2)) {
                 return "";
             }
 
             for (int j = 0; j < Math.min(word1.length(), word2.length()); j++) {
-                if (word1.charAt(j) != word2.charAt(j)) {
-                    adjList.get(word1.charAt(j)).add(word2.charAt(j));
-                    inorderMap.put(word2.charAt(j), inorderMap.get(word2.charAt(j)) + 1);
+                char c1 = word1.charAt(j), c2 = word2.charAt(j);
+
+                if (c1 != c2) {
+                    graph.get(c1).add(c2);
+                    inorder.put(c2, inorder.get(c2) + 1);
                     break;
                 }
             }
@@ -30,8 +35,8 @@ public String alienOrder(String[] words) {
         Queue<Character> q = new LinkedList<>();
         StringBuilder sb = new StringBuilder();
 
-        for (char c : inorderMap.keySet()) {
-            if (inorderMap.get(c) == 0) {
+        for (Character c : inorder.keySet()) {
+            if (inorder.get(c) == 0) {
                 q.offer(c);
             }
         }
@@ -40,17 +45,19 @@ public String alienOrder(String[] words) {
             char c = q.poll();
             sb.append(c);
 
-            for (char neighbour : adjList.get(c)) {
-                inorderMap.put(neighbour, inorderMap.get(neighbour) - 1);
-                if (inorderMap.get(neighbour) == 0) {
+            for (char neighbour : graph.get(c)) {
+                inorder.put(neighbour, inorder.get(neighbour) - 1);
+
+                if (inorder.get(neighbour) == 0) {
                     q.offer(neighbour);
                 }
             }
         }
 
-        if (sb.length() < inorderMap.size()) {
+        if (sb.length() < inorder.size()) {
             return "";
         }
+        ;
         return sb.toString();
     }
 }