Added graphValidTree solution

Author: nhistory

graph-valid-tree/nhistory.js

@@ -0,0 +1,46 @@
+class Solution {
+  /**
+   * @param {number} n
+   * @param {number[][]} edges
+   * @returns {boolean}
+   */
+  validTree(n, edges) {
+    // A valid tree must have exactly n - 1 edges
+    if (edges.length !== n - 1) {
+      return false;
+    }
+
+    // Initialize the adjacency list
+    let graph = [];
+    for (let i = 0; i < n; i++) {
+      graph.push([]);
+    }
+
+    // Populate the adjacency list with edges
+    for (let [node, neighbor] of edges) {
+      graph[node].push(neighbor);
+      graph[neighbor].push(node);
+    }
+
+    let visited = new Set();
+
+    // Depth-First Search (DFS) to explore the graph
+    function dfs(node) {
+      visited.add(node);
+      for (let neighbor of graph[node]) {
+        if (!visited.has(neighbor)) {
+          dfs(neighbor);
+        }
+      }
+    }
+
+    // Start DFS from node 0
+    dfs(0);
+
+    // Check if all nodes were visited
+    return visited.size === n;
+  }
+}
+
+// TC: O(n)
+// SC: O(n)