add Alien Dictionary solution

Author: HoonDongKang

alien-dictionary/HoonDongKang.ts

@@ -0,0 +1,75 @@
+/**
+ * [Problem]: [892] Alien Dictionary
+ * (https://www.lintcode.com/problem/892/)
+ */
+
+//시간복잡도 O(n+e)
+//공간복잡도 O(n+e)
+export class Solution {
+    /**
+     * @param words: a list of words
+     * @return: a string which is correct order
+     */
+    alienOrder(words: string[]): string {
+        // Write your code here
+        const graph: Map<string, Set<string>> = new Map();
+
+        // 모든 문자를 그래프 노드로 초기화
+        for (const word of words) {
+            for (const char of word) {
+                if (!graph.has(char)) {
+                    graph.set(char, new Set());
+                }
+            }
+        }
+
+        // 문자 간 선후관계(edge) 설정
+        for (let i = 1; i < words.length; i++) {
+            const prev = words[i - 1];
+            const curr = words[i];
+            let isDiff = false;
+
+            for (let j = 0; j < Math.min(prev.length, curr.length); j++) {
+                const p = prev[j];
+                const c = curr[j];
+
+                if (p !== c) {
+                    graph.get(p)!.add(c);
+                    isDiff = true;
+                    break;
+                }
+            }
+
+            if (!isDiff && prev.length > curr.length) {
+                return "";
+            }
+        }
+
+        const visited: Set<string> = new Set();
+        const visiting: Set<string> = new Set();
+        const output: string[] = [];
+
+        function dfs(node: string): boolean {
+            if (visited.has(node)) return true;
+            if (visiting.has(node)) return false;
+
+            visiting.add(node);
+
+            for (const neighbor of graph.get(node)!) {
+                if (!dfs(neighbor)) return false;
+            }
+
+            visiting.delete(node);
+            visited.add(node);
+            output.push(node);
+
+            return true;
+        }
+
+        for (const node of graph.keys()) {
+            if (!dfs(node)) return "";
+        }
+
+        return output.reverse().join("");
+    }
+}