java: add «648. Replace Words»

Signed-off-by: Matej Focko <me@mfocko.xyz>

java/replace-words.java

@@ -0,0 +1,78 @@
+import java.util.List;
+
+class Solution {
+  private class Trie {
+    public Trie() {
+      root = new TrieNode();
+    }
+
+    public void insert(String word) {
+      root.insert(word);
+    }
+
+    public String shortestPrefix(String word) {
+      return root.shortestPrefix(word);
+    }
+
+    private TrieNode root;
+
+    private class TrieNode {
+      boolean has;
+      TrieNode[] successors;
+
+      TrieNode() {
+        has = false;
+        successors = new TrieNode[26];
+      }
+
+      void insert(String word) {
+        TrieNode node = this;
+
+        for (int i = 0; i < word.length(); ++i) {
+          int idx = word.charAt(i) - 'a';
+
+          if (node.successors[idx] == null) {
+            node.successors[idx] = new TrieNode();
+          }
+          node = node.successors[idx];
+        }
+
+        node.has = true;
+      }
+
+      String shortestPrefix(String word) {
+        TrieNode node = this;
+
+        for (int i = 0; i < word.length(); ++i) {
+          int idx = word.charAt(i) - 'a';
+
+          if (node.successors[idx] == null) {
+            return word;
+          }
+
+          node = node.successors[idx];
+          if (node.has) {
+            return word.substring(0, i + 1);
+          }
+        }
+
+        return word;
+      }
+    }
+  }
+
+  public String replaceWords(List<String> dictionary, String sentence) {
+    String words[] = sentence.split(" ");
+
+    var t = new Trie();
+    for (var word : dictionary) {
+      t.insert(word);
+    }
+
+    for (int i = 0; i < words.length; ++i) {
+      words[i] = t.shortestPrefix(words[i]);
+    }
+
+    return String.join(" ", words);
+  }
+}