advance tree questions

Author: kunal-kushwaha

lectures/20-trees/code/Advance questions/Main.java

@@ -0,0 +1,5 @@
+class Main {
+  public static void main(String[] args) {
+
+  }
+}

lectures/20-trees/code/Advance questions/PreIn.java

@@ -0,0 +1,34 @@
+class PreIn {
+
+  public TreeNode buildTree(int[] preOrder, int[] inOrder) {
+    HashMap<Integer, Integer> map = new HashMap<>();
+
+    for(int i=0; i < inOrder.length; i++) {
+      map.put(inOrder[i], i);
+    }
+
+    int[] index = {0};
+    
+    return helper(preOrder, inOrder, 0, preOrder.length-1, map, index);
+  }
+
+  public TreeNode helper(int[] preOrder, int[] inOrder, int left, int right, HashMap<Integer, Integer> map, int[] index) {
+    if (left > right) {
+      return null;
+    }
+
+    int current = preOrder[index[0]];
+    index[0]++;
+
+    TreeNode node = new TreeNode(current);
+
+    if (left == right) {
+      return node;
+    }
+
+    node.left = helper(preOrder, inOrder, left, index - 1, map, index);
+    node.right = helper(preOrder, inOrder, index + 1, right, map, index);
+
+    return node;
+  }
+}

lectures/20-trees/code/Advance questions/VerticalTraversal.java

@@ -0,0 +1,45 @@
+class VerticalTraversal {
+  public List<List<Integer>> verticalTraversal(TreeNode node) {
+    List<List<Integer>> ans = new ArrayList<List<Integer>>();
+
+    if (node == null) {
+      return ans;
+    }
+
+    int col = 0;
+
+    Queue<Map.Entry<TreeNode, Integer>> queue = new ArrayDeque<>();
+    Map<Integer, ArrayList<Integer>> map = new HashMap();
+
+    queue.offer(new AbstractMap.SimpleEntry<>(node, col));
+
+    int min = 0;
+    int max = 0;
+
+    while(!queue.isEmpty()) {
+      Map.Entry<TreeNode, Integer> removed = queue.poll();
+      node = removed.getKey();
+      col = removed.getValue();
+
+      if(node != null) {
+        if(!map.containsKey(col)) {
+          map.put(col, new ArrayList<Integer>());
+        }
+
+        map.get(col).add(node.val);
+
+        min = Math.min(min, col);
+        max = Math.max(max, col);
+
+        queue.offer(new AbstractMap.SimpleEntry<>(node.left, col-1));
+        queue.offer(new AbstractMap.SimpleEntry<>(node.right, col+1));
+      }
+    }
+
+    for(int i=min; i <= max; i++) {
+      ans.add(map.get(i));
+    }
+
+    return ans;
+  }
+}

lectures/20-trees/code/Advance questions/WordLadder.java

@@ -0,0 +1,39 @@
+public class WordLadder {
+    public static int ladderLength(String beginWord, String endWord, List<String> wordList) {
+        if (!wordList.contains(endWord))
+            return 0;
+
+        Set<String> visited = new HashSet<>();
+        Queue<String> q = new LinkedList<>();
+        q.offer(beginWord);
+        int length = 0;
+
+        while (!q.isEmpty()) {
+            int size = q.size();
+            length++;
+
+            for (int i = 0; i < size; i++) {
+                String current = q.poll();
+
+                for (int j = 0; j < current.length(); j++) {
+                    char[] temp = current.toCharArray();
+
+                    for (char c = 'a'; c <= 'z'; c++) {
+                        temp[j] = c;
+                        String newWord = new String(temp);
+
+                        if (newWord.equals(endWord))
+                            return length + 1;
+
+                        if (wordList.contains(newWord) && !visited.contains(newWord)) {
+                            q.offer(newWord);
+                            visited.add(newWord);
+                        }
+                    }
+                }
+            }
+        }
+
+        return 0;
+    }
+}