fix: move problem into category

Hard/longest-cycle-in-a-graph/Solution.java

@@ -0,0 +1,29 @@
+class Solution {
+    public int longestCycle(int[] edges) {
+        int[] visited = new int[edges.length];
+        int max = -1;
+
+        for (int i = 0; i < edges.length; ++i) {
+            if (visited[i] > 0) {
+                continue;
+            }
+
+            int current = i;
+            while (current != -1 && visited[current] == 0) {
+                visited[current] = i + 1;
+                current = edges[current];
+            }
+
+            if (current != -1 && visited[current] == i + 1) {
+                int cycle = 1;
+                int temp = edges[current];
+                while (temp != current) {
+                    ++cycle;
+                    temp = edges[temp];
+                }
+                max = max > cycle ? max : cycle;
+            }
+        }
+        return max;
+    }
+}