[ PS ] : Alien Dictionary

Author: uraflower

alien-dictionary/uraflower.js

@@ -0,0 +1,74 @@
+/**
+ * @param words: a list of words
+ * @return: a string which is correct order
+ */
+const alienOrder = (words) => {
+  const graph = {};
+
+  // 초기화
+  for (const word of words) {
+    for (const char of word) {
+      if (!graph[char]) {
+        graph[char] = new Set();
+      }
+    }
+  }
+
+  // 그래프 생성
+  for (let i = 1; i < words.length; i++) {
+    const prev = words[i - 1];
+    const current = words[i];
+    let found = false;
+
+    const minLen = Math.min(prev.length, current.length);
+    for (let j = 0; j < minLen; j++) {
+      graph[prev[j]].add(current[j]);
+    }
+    // 모순 처리
+    if (!found && prev.length > current.length) {
+      return '';
+    }
+  }
+
+  // 탐색
+  const output = [];
+  const visiting = new Set();
+  const visited = new Set();
+
+  function dfs(current) {
+    if (visiting.has(current)) {
+      return false;
+    }
+    if (visited.has(current)) {
+      return true;
+    }
+
+    visiting.add(current);
+    for (const adj of graph[current]) {
+      if (!dfs(adj)) {
+        return false;
+      }
+    }
+    visiting.delete(current);
+
+    visited.add(current);
+    output.push(current);
+    return true;
+  }
+
+  // 순회
+  for (const node in graph) {
+    if (!dfs(node)) {
+      return '';
+    }
+  }
+
+  return output.reverse().join('')
+}
+
+
+// 방향 그래프로 선행되는 순서를 표현
+// 비슷한 문제: https://leetcode.com/problems/course-schedule/description/
+
+// 위상정렬 사용해서 진입차수 기준 정렬하는 방법도 있음
+// 너무 어려웠다...