Create 802.cpp

Author: JanaSabuj

802/802.cpp

@@ -0,0 +1,39 @@
+class Solution {
+public:
+    
+    enum Color{
+        white,
+        gray,
+        black
+    };
+    
+    int dfs(vector<vector<int>>& graph, vector<int>& color, int x){
+        
+        // base
+        if(color[x]) 
+            return color[x] == black;// safe
+                
+        // main
+        color[x] = gray;        
+        for(auto v: graph[x]){
+            if(!dfs(graph, color, v))
+                return false;
+        }
+        color[x] = black;
+        return true;      
+    }
+    
+    vector<int> eventualSafeNodes(vector<vector<int>>& graph) {
+        int n = graph.size();
+        vector<int> color(n, white);
+        
+        // dfs that returns safe/unsafe
+        vector<int> safe;
+        for(int i = 0; i < n; i++){
+           if(dfs(graph, color, i))
+               safe.push_back(i);
+        }
+        
+        return safe;
+    }
+};