Added 1 solution & modified 1 solution

Author: varunu28

Easy/Power of Two.java

@@ -0,0 +1,23 @@
+class Solution {
+  public boolean isPowerOfTwo(int n) {
+    if (n % 2 != 0 && n != 1) {
+      return false;
+    }
+    int start = 0;
+    int end = n / 2;
+    while (start <= end) {
+      int mid = (start + end) / 2;
+      int pow = (int) (Math.pow(2, mid));
+      if (n == pow) {
+        return true;
+      }
+      else if (n > pow) {
+        start = mid + 1;
+      }
+      else {
+        end = mid - 1;
+      }
+    }
+    return false;
+  }
+}

Easy/power_of_2.java

@@ -0,0 +1,47 @@
+class BrowserHistory {
+  
+  Node root;
+  public BrowserHistory(String homepage) {
+    root = new Node(homepage);
+  }
+
+  public void visit(String url) {
+    Node node = new Node(url);
+    root.next = null;
+    root.next = node;
+    node.prev = root;
+    root = root.next;
+  }
+
+  public String back(int steps) {
+    while (steps-- > 0 && root.prev != null) {
+      root = root.prev;
+    }
+    return root.val;
+  }
+
+  public String forward(int steps) {
+    while (steps-- > 0 && root.next != null) {
+      root = root.next;
+    }
+    return root.val;
+  }
+}
+
+class Node {
+  String val;
+  Node next;
+  Node prev;
+  
+  public Node(String val) {
+    this.val = val;
+  }
+}
+
+/**
+ * Your BrowserHistory object will be instantiated and called as such:
+ * BrowserHistory obj = new BrowserHistory(homepage);
+ * obj.visit(url);
+ * String param_2 = obj.back(steps);
+ * String param_3 = obj.forward(steps);
+ */