Alien Dictionary

Author: charlesbuczel

0269_alienDictionary.js

@@ -0,0 +1,60 @@
+/**
+ * @param {string[]} words Array of strings.
+ * @return {string} String containing letters in order for alien language.
+ * @summary Alien Dictionary {@link https://leetcode.com/problems/alien-dictionary/}
+ * @description Given a list of words in alien dictionary which are sorted by rules of the language, return the order of letters in the language.
+ * Space O(1) - store number of relations and at mosat unique records for number of unique chars.
+ * Time O(n) - where n is the length of all of the words combined.
+ */
+const alienOrder = words => {
+  const adjList = {};
+  const counts = {};
+
+  for (let i = 0; i < words.length; i++) {
+    const word = words[i];
+    for (let j = 0; j < word.length; j++) {
+      const char = word[j];
+
+      adjList[char] = [];
+      counts[char] = 0;
+    }
+  }
+
+  for (let i = 0; i < words.length - 1; i++) {
+    const w1 = words[i];
+    const w2 = words[i + 1];
+
+    if (w1.length > w2.length && !w1.indexOf(w2)) {
+      return '';
+    }
+
+    for (let j = 0; j < Math.min(w1.length, w2.length); j++) {
+      const c1 = w1[j];
+      const c2 = w2[j];
+      if (c1 !== c2) {
+        adjList[w1[j]].push(w2[j]);
+        counts[w2[j]]++;
+        break;
+      }
+    }
+  }
+
+  const answer = [];
+  const queue = [];
+
+  Object.keys(counts).forEach(char => {
+    if (!counts[char]) queue.push(char);
+  });
+
+  while (queue.length) {
+    const char = queue.pop();
+    answer.push(char);
+
+    (adjList[char] || []).forEach(adjacent => {
+      counts[adjacent]--;
+      if (!counts[adjacent]) queue.unshift(adjacent);
+    });
+  }
+
+  return answer.length < Object.keys(counts).length ? '' : answer.join('');
+};