MEDIUM/src/medium/BinaryTreeVerticalOrderTraversal.java

Author: fishercoder1534

MEDIUM/src/medium/BinaryTreeVerticalOrderTraversal.java

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+package medium;
+
+import classes.TreeNode;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Map;
+import java.util.Queue;
+import java.util.TreeMap;
+
+public class BinaryTreeVerticalOrderTraversal {
+    public List<List<Integer>> verticalOrder_using_treemap(TreeNode root) {
+        List<List<Integer>> result = new ArrayList();
+        if(root == null) return result;
+        Queue<TreeNode> bfsQ = new LinkedList();
+        Queue<Integer> indexQ = new LinkedList();
+        TreeMap<Integer, List<Integer>> map = new TreeMap();
+        bfsQ.offer(root);
+        indexQ.offer(0);//we set the root as index 0, left will be negative, right will be positive
+        while(!bfsQ.isEmpty()){
+            int qSize = bfsQ.size();
+            for(int i = 0; i < qSize; i++){
+                TreeNode curr = bfsQ.poll();
+                int index = indexQ.poll();
+                if(map.containsKey(index)){
+                    map.get(index).add(curr.val);
+                } else if(!map.containsKey(index)){
+                    List<Integer> list = new ArrayList();
+                    list.add(curr.val);
+                    map.put(index, list);
+                }
+                if(curr.left != null){
+                    bfsQ.offer(curr.left);
+                    indexQ.offer(index-1);
+                }
+                if(curr.right != null){
+                    bfsQ.offer(curr.right);
+                    indexQ.offer(index+1);
+                }
+            }
+        }
+        for(int i : map.keySet()){
+            result.add(map.get(i));
+        }
+        return result;
+    }
+
+    public List<List<Integer>> verticalOrder_using_hashmap(TreeNode root) {
+        List<List<Integer>> result = new ArrayList();
+        if(root == null) return result;
+        Queue<TreeNode> bfsQ = new LinkedList();
+        Queue<Integer> indexQ = new LinkedList();
+        HashMap<Integer, List<Integer>> map = new HashMap();
+        bfsQ.offer(root);
+        indexQ.offer(0);//we set the root as index 0, left will be negative, right will be positive
+        int min = 0, max = 0;
+        while(!bfsQ.isEmpty()){
+            int qSize = bfsQ.size();
+            for(int i = 0; i < qSize; i++){
+                TreeNode curr = bfsQ.poll();
+                int index = indexQ.poll();
+                if(map.containsKey(index)){
+                    map.get(index).add(curr.val);
+                } else if(!map.containsKey(index)){
+                    List<Integer> list = new ArrayList();
+                    list.add(curr.val);
+                    map.put(index, list);
+                }
+                if(curr.left != null){
+                    bfsQ.offer(curr.left);
+                    indexQ.offer(index-1);
+                    min  = Math.min(min, index-1);
+                }
+                if(curr.right != null){
+                    bfsQ.offer(curr.right);
+                    indexQ.offer(index+1);
+                    max = Math.max(max, index+1);
+                }
+            }
+        }
+        for(int i = min; i <= max; i++){
+            result.add(map.get(i));
+        }
+        return result;
+    }
+
+}