0324

Author: surajr

java/findRepeatedDnaSequences.java

@@ -0,0 +1,17 @@
+class Solution {
+    public List<String> findRepeatedDnaSequences(String s) {
+        Map<String, Integer> map = new HashMap<>();
+        Set<String> result = new HashSet<>();
+        
+        if(s.length() < 10) return new ArrayList<String>(result);
+        
+        for(int i=0; i<=s.length()-10; i++){
+            String substr = s.substring(i, i+10);
+            map.put(substr, map.getOrDefault(substr, 0)+1);
+            if(map.get(substr)>1)
+                result.add(substr);            
+        }
+                
+        return new ArrayList<String>(result);
+    }
+}

java/isUnivalTree.java

@@ -0,0 +1,65 @@
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode(int x) { val = x; }
+ * }
+ */
+class Solution {
+    /*
+    Recursion: Do a DFS recursively 
+    Time & Space: O(n)
+    
+    */
+    
+    public boolean isUnivalTree(TreeNode root) {
+        if(root == null)
+            return true;
+        
+        return dfs(root, root.val);
+        
+    }
+    
+    public boolean dfs(TreeNode node, int val){
+        if(node == null)
+            return true;
+        if(node.val != val)
+            return false;
+        return dfs(node.left, val) && dfs(node.right, val);
+    }
+
+
+/*
+
+Approach 2: Iteratively 
+Time and Space: O(n)
+*/
+
+    public boolean isUnivalTree(TreeNode root) {
+        if(root == null)
+            return true;
+        
+        Queue<TreeNode> queue = new LinkedList<>();
+        queue.add(root);
+        
+        while(!queue.isEmpty()){
+            int size = queue.size();
+            TreeNode node = queue.remove();
+            
+            if(root.val != node.val) 
+                return false;
+            
+            if(node.left != null) queue.add(node.left);
+            if(node.right != null) queue.add(node.right);
+            
+        }
+        
+        return true;
+    }
+}
+
+
+
+