add Graph Valid Tree solution

Author: HoonDongKang

graph-valid-tree/HoonDongKang.ts

@@ -0,0 +1,65 @@
+/**
+ * [Problem]: [178] Graph Valid Tree
+ * (https://www.lintcode.com/problem/178/)
+ */
+
+export class Solution {
+    /**
+     * @param n: An integer
+     * @param edges: a list of undirected edges
+     * @return: true if it's a valid tree, or false
+     */
+    //시간복잡도 O(n+e)
+    //공간복잡도 O(n+e)
+    validTree(n: number, edges: number[][]): boolean {
+        const graph: number[][] = Array.from({ length: n }, () => []);
+        for (const [a, b] of edges) {
+            graph[a].push(b);
+            graph[b].push(a);
+        }
+
+        const visited = new Set<number>();
+
+        function hasCycle(node: number, prev: number): boolean {
+            if (visited.has(node)) return true;
+            visited.add(node);
+
+            for (const neighbor of graph[node]) {
+                if (neighbor === prev) continue;
+                if (hasCycle(neighbor, node)) return true;
+            }
+            return false;
+        }
+
+        if (hasCycle(0, -1)) return false;
+
+        return visited.size === n;
+    }
+
+    //시간복잡도 O(n)
+    //공간복잡도 O(n)
+    validTree2(n: number, edges: number[][]): boolean {
+        if (edges.length !== n - 1) return false;
+
+        const graph: number[][] = Array.from({ length: n }, () => []);
+        for (const [a, b] of edges) {
+            graph[a].push(b);
+            graph[b].push(a);
+        }
+
+        const visited = new Set<number>();
+
+        function dfs(node: number) {
+            visited.add(node);
+            for (const neighbor of graph[node]) {
+                if (!visited.has(neighbor)) {
+                    dfs(neighbor);
+                }
+            }
+        }
+
+        dfs(0);
+
+        return visited.size === n;
+    }
+}