update 802 java

Author: yennanliu

leetcode_java/src/main/java/LeetCodeJava/DFS/FindEventualSafeStates.java

@@ -74,6 +74,12 @@ public class FindEventualSafeStates {
     public List<Integer> eventualSafeNodes(int[][] graph) {
         // init
         int n = graph.length;
+        /**
+         *  NOTE !!!
+         *
+         *   we init status array (states)
+         *   and set all init value as "UNKNOWN"
+         */
         State[] states = new State[n];
         for (int i = 0; i < n; i++) {
             states[i] = State.UNKNOWN;
@@ -82,6 +88,11 @@ public List<Integer> eventualSafeNodes(int[][] graph) {
         List<Integer> result = new ArrayList<>();
         for (int i = 0; i < n; i++) {
             // if node is with SAFE state, add to result
+            /**
+             *  NOTE !!!
+             *
+             *   the dfs parameter: we use index, state array as well
+             */
             if (dfs(graph, i, states) == State.SAFE) {
                 result.add(i);
             }
@@ -100,6 +111,12 @@ private State dfs(int[][] graph, int node, State[] states) {
          *  but is visited again (within the other iteration)
          *  -> there must be a cycle
          *  -> this node is UNSAFE
+         *
+         *
+         *  NOTE !!!
+         *
+         *   we DON'T compare current status,
+         *   but compare state (states[node]) via index, and enum
          */
         if (states[node] == State.VISITING) {
             return states[node] = State.UNSAFE;
@@ -108,6 +125,10 @@ private State dfs(int[][] graph, int node, State[] states) {
          * NOTE !!!
          *  if a node is not with "UNKNOWN" state,
          *  -> update its state
+         *
+         *   NOTE !!!
+         *   we DON'T compare current status,
+         *   but compare state (states[node]) via index, and enum
          */
         if (states[node] != State.UNKNOWN) {
             return states[node];
@@ -121,7 +142,7 @@ private State dfs(int[][] graph, int node, State[] states) {
         for (int next : graph[node]) {
             /**
              * NOTE !!!
-             *   for every sub node, if any one them
+             *   for every sub node, if any of them
              *   has UNSAFE state,
              *   -> set and return node state as UNSAFE directly
              */

leetcode_java/src/main/java/dev/workspace5.java

@@ -2201,11 +2201,55 @@ public boolean isNStraightHand(int[] hand, int groupSize) {
     }
 
     // LC 802
-    // 5,28 - 5.40 PM
+    // 6.15 pm - 6.30
     // https://leetcode.com/problems/find-eventual-safe-states/
+    // dfs
+    List<String> states = new ArrayList<>();
     public List<Integer> eventualSafeNodes(int[][] graph) {
 
-        return null;
+        for (int i = 0; i < graph.length; i++){
+            states.add("UNKNOWN");
+        }
+
+        if (graph.length==0){
+            return null;
+        }
+
+        List<Integer> res = new ArrayList<>();
+
+        for (int i = 0; i < graph.length; i++){
+            if (isSafe(i, graph)){
+               res.add(i);
+            }
+        }
+
+        return res;
+    }
+
+    // 4 states : UNKNOWN, VISITING, SAFE, UNSAFE
+    private boolean isSafe(int idx, int[][] graph){
+        String curState = states.get(idx);
+        if (curState.equals("SAFE")){
+            return true;
+        }
+        if (curState.equals("VISITING")){
+            return false;
+        }
+        // TODO : check
+//        if (!curState.equals("UNKNOWN")){
+//            return curState.equals("SAFE"); // ??
+//        }
+
+        curState = "VISITING";
+
+        for (int j = 0; j < graph.length; j++){
+            if (!this.isSafe(j, graph)){
+                return false;
+            }
+        }
+
+        //curState =
+        return true; // ??? curState.equals("SAFE"); // ??
     }
 
     // LC 1197