Added 1 solution & modified 1 solution

varunu28 · varunu28 · commit 712e6dffd99b · 2020-08-04T08:10:35.000-05:00
diff --git a/Easy/Power of four.java b/Easy/Power of four.java
@@ -1,5 +1,20 @@
 class Solution {
-    public boolean isPowerOfFour(int num) {
-        return num>0 && (num&(num - 1))== 0 && (num-1)%3 == 0;
+  public boolean isPowerOfFour(int num) {
+    long start = 0;
+    long end = num / 4;
+    while (start <= end) {
+      long mid = (start + end) / 2;
+      long pow = (long) Math.pow(4, mid);
+      if (pow == (long) num) {
+        return true;
+      }
+      else if (pow > (long) num) {
+        end = mid - 1;
+      }
+      else {
+        start = mid + 1;
+      }
     }
+    return false;
+  }
 }
diff --git a/Medium/All Paths from Source Lead to Destination.java b/Medium/All Paths from Source Lead to Destination.java
@@ -0,0 +1,33 @@
+class Solution {
+  enum State { 
+    PROCESSING, 
+    PROCESSED 
+  }
+  
+  public boolean leadsToDestination(int n, int[][] edges, int source, int destination) {
+    Map<Integer, Set<Integer>> graph = new HashMap<>();
+    for (int[] edge : edges) {
+      graph.computeIfAbsent(edge[0], k -> new HashSet<>()).add(edge[1]);
+    }
+    return leadsToDestinationHelper(graph, source, destination, new State[n]);
+  }
+  
+  private boolean leadsToDestinationHelper(
+    Map<Integer, Set<Integer>> graph, int source, int destination, State[] states
+  ) {
+    if (states[source] != null) {
+      return states[source] == State.PROCESSED;
+    }
+    if (!graph.containsKey(source)) {
+      return source == destination;
+    }
+    states[source] = State.PROCESSING;
+    for (Integer child : graph.getOrDefault(source, new HashSet<>())) {
+      if (!leadsToDestinationHelper(graph, child, destination, states)) {
+        return false;
+      }
+    }
+    states[source] = State.PROCESSED;
+    return true;
+  }
+}
